From: Qemu-arm [mailto:qemu-arm-bounces+salil.mehta=huawei.com@nongnu.org] On Behalf Of wangyanan (Y) Sent: Thursday, May 13, 2021 6:10 AM
Hi Drew,
I got a question below, and hope your reply. Thanks! On 2021/4/13 16:07, Yanan Wang wrote:
Add the Processor Properties Topology Table (PPTT) to present CPU topology information to ACPI guests. Note, while a DT boot Linux guest with a non-flat CPU topology will see socket and core IDs being sequential integers starting from zero, e.g. with -smp 4,sockets=2,cores=2,threads=1
a DT boot produces
cpu: 0 package_id: 0 core_id: 0 cpu: 1 package_id: 0 core_id: 1 cpu: 2 package_id: 1 core_id: 0 cpu: 3 package_id: 1 core_id: 1
an ACPI boot produces
cpu: 0 package_id: 36 core_id: 0 cpu: 1 package_id: 36 core_id: 1 cpu: 2 package_id: 96 core_id: 2 cpu: 3 package_id: 96 core_id: 3
This is due to several reasons:
DT cpu nodes do not have an equivalent field to what the PPTT ACPI Processor ID must be, i.e. something equal to the MADT CPU UID or equal to the UID of an ACPI processor container. In both ACPI cases those are platform dependant IDs assigned by the vendor.
While QEMU is the vendor for a guest, if the topology specifies SMT (> 1 thread), then, with ACPI, it is impossible to assign a core-id the same value as a package-id, thus it is not possible to have package-id=0 and core-id=0. This is because package and core containers must be in the same ACPI namespace and therefore must have unique UIDs.
ACPI processor containers are not required for PPTT tables to be used and, due to the limitations of which IDs are selected described above in (2), they are not helpful for QEMU, so we don't build them with this patch. In the absence of them, Linux assigns its own unique IDs. The maintainers have chosen not to use counters from zero, but rather ACPI table offsets, which explains why the numbers are so much larger than with DT.
When there is no SMT (threads=1) the core IDs for ACPI boot guests match the logical CPU IDs, because these IDs must be equal to the MADT CPU UID (as no processor containers are present), and QEMU uses the logical CPU ID for these MADT IDs.
Tested-by: Jiajie Li lijiajie11@huawei.com Signed-off-by: Andrew Jones drjones@redhat.com Signed-off-by: Ying Fang fangying1@huawei.com Signed-off-by: Yanan Wang wangyanan55@huawei.com
hw/arm/virt-acpi-build.c | 63 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 63 insertions(+)
diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c index 2ad5dad1bf..03fd812d5a 100644 --- a/hw/arm/virt-acpi-build.c +++ b/hw/arm/virt-acpi-build.c @@ -436,6 +436,64 @@ build_srat(GArray *table_data, BIOSLinker *linker,
VirtMachineState *vms)
vms->oem_table_id);}
+/* PPTT */ +static void +build_pptt(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms) +{
- int pptt_start = table_data->len;
- int uid = 0, cpus = 0, socket = 0;
- MachineState *ms = MACHINE(vms);
- unsigned int smp_cores = ms->smp.cores;
- unsigned int smp_threads = ms->smp.threads;
- acpi_data_push(table_data, sizeof(AcpiTableHeader));
- for (socket = 0; cpus < ms->possible_cpus->len; socket++) {
uint32_t socket_offset = table_data->len - pptt_start;int core;build_processor_hierarchy_node(table_data, 1, /* Physical package */0, socket, /* No parent */NULL, 0); /* No private resources */for (core = 0; core < smp_cores; core++) {uint32_t core_offset = table_data->len - pptt_start;int thread;if (smp_threads <= 1) {build_processor_hierarchy_node(table_data,(1 << 1) | /* ACPI Processor ID valid */(1 << 3), /* ACPI 6.3 - Node is a Leaf */socket_offset, uid++, /* Parent is a Socket */NULL, 0); /* No private resources */} else {build_processor_hierarchy_node(table_data, 0,socket_offset, core, /* Parent is a Socket */NULL, 0); /* No private resources */for (thread = 0; thread < smp_threads; thread++) {build_processor_hierarchy_node(table_data,(1 << 1) | /* ACPI Processor ID valid */(1 << 2) | /* ACPI 6.3 - Processor is a Thread */(1 << 3), /* ACPI 6.3 - Node is a Leaf */core_offset, uid++, /* Parent is a Core */NULL, 0); /* No private resources */}}}cpus += smp_cores * smp_threads;- }
- build_header(linker, table_data,
(void *)(table_data->data + pptt_start), "PPTT",table_data->len - pptt_start, 2,vms->oem_id, vms->oem_table_id);+}
- /* GTDT */ static void build_gtdt(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
@@ -707,6 +765,11 @@ void virt_acpi_build(VirtMachineState *vms,
AcpiBuildTables *tables)
acpi_add_table(table_offsets, tables_blob); build_madt(tables_blob, tables->linker, vms);
- if (ms->smp.cpus > 1 && !vmc->no_cpu_topology) {
I'm not really sure why we need to care about "ms->smp.cpus > 1" here?
IMO, just like MADT in which we create both ENABLED and DISABLED gicc nodes no matter of number of ENABLED nodes is one or not, we should create PPTT table for all the possible cpus and not care about number of smp cpus, too. This will be more consistent with the ACPI specification and the PPTT table will be used for ACPI cpu hotplug in the future even with "smp.cpus == 1".
A humble request: Let us not anticipate the changes of vcpu Hotplug here. Things are fluid with respect to the vcpu Hotplug right now and I think it will not be right to base PPTT Table changes in anticipation of something we are not sure of what it looks like.
Any such decisions should be postponed and be made part of the actual vcpu Hotplug changes when(and if ever) they come for ARM64. This will also ensure proper review of such changes and useful in that particular context.
Thanks
Care of "smp.cpus > 1" in the DT cpu-map part makes sense to me, because we are required to only add present cpu nodes to the DT and Linux Doc says that a cpu-map is not needed for uniprocessor systems.
Thanks, Yanan
acpi_add_table(table_offsets, tables_blob);build_pptt(tables_blob, tables->linker, vms);- }
acpi_add_table(table_offsets, tables_blob); build_gtdt(tables_blob, tables->linker, vms);
On Tue, May 18, 2021 at 07:17:56AM +0000, Salil Mehta wrote:
From: Qemu-arm [mailto:qemu-arm-bounces+salil.mehta=huawei.com@nongnu.org] On Behalf Of wangyanan (Y) Sent: Thursday, May 13, 2021 6:10 AM
Hi Drew,
I got a question below, and hope your reply. Thanks! On 2021/4/13 16:07, Yanan Wang wrote:
Add the Processor Properties Topology Table (PPTT) to present CPU topology information to ACPI guests. Note, while a DT boot Linux guest with a non-flat CPU topology will see socket and core IDs being sequential integers starting from zero, e.g. with -smp 4,sockets=2,cores=2,threads=1
a DT boot produces
cpu: 0 package_id: 0 core_id: 0 cpu: 1 package_id: 0 core_id: 1 cpu: 2 package_id: 1 core_id: 0 cpu: 3 package_id: 1 core_id: 1
an ACPI boot produces
cpu: 0 package_id: 36 core_id: 0 cpu: 1 package_id: 36 core_id: 1 cpu: 2 package_id: 96 core_id: 2 cpu: 3 package_id: 96 core_id: 3
This is due to several reasons:
DT cpu nodes do not have an equivalent field to what the PPTT ACPI Processor ID must be, i.e. something equal to the MADT CPU UID or equal to the UID of an ACPI processor container. In both ACPI cases those are platform dependant IDs assigned by the vendor.
While QEMU is the vendor for a guest, if the topology specifies SMT (> 1 thread), then, with ACPI, it is impossible to assign a core-id the same value as a package-id, thus it is not possible to have package-id=0 and core-id=0. This is because package and core containers must be in the same ACPI namespace and therefore must have unique UIDs.
ACPI processor containers are not required for PPTT tables to be used and, due to the limitations of which IDs are selected described above in (2), they are not helpful for QEMU, so we don't build them with this patch. In the absence of them, Linux assigns its own unique IDs. The maintainers have chosen not to use counters from zero, but rather ACPI table offsets, which explains why the numbers are so much larger than with DT.
When there is no SMT (threads=1) the core IDs for ACPI boot guests match the logical CPU IDs, because these IDs must be equal to the MADT CPU UID (as no processor containers are present), and QEMU uses the logical CPU ID for these MADT IDs.
Tested-by: Jiajie Li lijiajie11@huawei.com Signed-off-by: Andrew Jones drjones@redhat.com Signed-off-by: Ying Fang fangying1@huawei.com Signed-off-by: Yanan Wang wangyanan55@huawei.com
hw/arm/virt-acpi-build.c | 63 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 63 insertions(+)
diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c index 2ad5dad1bf..03fd812d5a 100644 --- a/hw/arm/virt-acpi-build.c +++ b/hw/arm/virt-acpi-build.c @@ -436,6 +436,64 @@ build_srat(GArray *table_data, BIOSLinker *linker,
VirtMachineState *vms)
vms->oem_table_id);}
+/* PPTT */ +static void +build_pptt(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms) +{
- int pptt_start = table_data->len;
- int uid = 0, cpus = 0, socket = 0;
- MachineState *ms = MACHINE(vms);
- unsigned int smp_cores = ms->smp.cores;
- unsigned int smp_threads = ms->smp.threads;
- acpi_data_push(table_data, sizeof(AcpiTableHeader));
- for (socket = 0; cpus < ms->possible_cpus->len; socket++) {
uint32_t socket_offset = table_data->len - pptt_start;int core;build_processor_hierarchy_node(table_data, 1, /* Physical package */0, socket, /* No parent */NULL, 0); /* No private resources */for (core = 0; core < smp_cores; core++) {uint32_t core_offset = table_data->len - pptt_start;int thread;if (smp_threads <= 1) {build_processor_hierarchy_node(table_data,(1 << 1) | /* ACPI Processor ID valid */(1 << 3), /* ACPI 6.3 - Node is a Leaf */socket_offset, uid++, /* Parent is a Socket */NULL, 0); /* No private resources */} else {build_processor_hierarchy_node(table_data, 0,socket_offset, core, /* Parent is a Socket */NULL, 0); /* No private resources */for (thread = 0; thread < smp_threads; thread++) {build_processor_hierarchy_node(table_data,(1 << 1) | /* ACPI Processor ID valid */(1 << 2) | /* ACPI 6.3 - Processor is a Thread */(1 << 3), /* ACPI 6.3 - Node is a Leaf */core_offset, uid++, /* Parent is a Core */NULL, 0); /* No private resources */}}}cpus += smp_cores * smp_threads;- }
- build_header(linker, table_data,
(void *)(table_data->data + pptt_start), "PPTT",table_data->len - pptt_start, 2,vms->oem_id, vms->oem_table_id);+}
- /* GTDT */ static void build_gtdt(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
@@ -707,6 +765,11 @@ void virt_acpi_build(VirtMachineState *vms,
AcpiBuildTables *tables)
acpi_add_table(table_offsets, tables_blob); build_madt(tables_blob, tables->linker, vms);
- if (ms->smp.cpus > 1 && !vmc->no_cpu_topology) {
I'm not really sure why we need to care about "ms->smp.cpus > 1" here?
IMO, just like MADT in which we create both ENABLED and DISABLED gicc nodes no matter of number of ENABLED nodes is one or not, we should create PPTT table for all the possible cpus and not care about number of smp cpus, too. This will be more consistent with the ACPI specification and the PPTT table will be used for ACPI cpu hotplug in the future even with "smp.cpus == 1".
A humble request: Let us not anticipate the changes of vcpu Hotplug here. Things are fluid with respect to the vcpu Hotplug right now and I think it will not be right to base PPTT Table changes in anticipation of something we are not sure of what it looks like.
Any such decisions should be postponed and be made part of the actual vcpu Hotplug changes when(and if ever) they come for ARM64. This will also ensure proper review of such changes and useful in that particular context.
Hi Salil,
Can you please elaborate on this and send some pointers to the hot plug discussions? You're not saying that we shouldn't try to generate PPTT tables for AArch64 guests until a solution for hot plug has been determined, are you? If so, I don't think I would agree with that. There are benefits to properly describing cpu topology to guests, even without hot plug. Those benefits, when vcpu pinning is used, are the same benefits as for the host, which already use PPTT tables to describe topology, even though hot plug isn't supported.
Now, if you're saying we should only generate tables for smp.cpus, not smp.maxcpus, because hot plug isn't supported anyway, then I see your point. But, it'd be better to require smp.cpus == smp.maxcpus in our smp_parse function to do that, which we've never done before, so we may have trouble supporting existing command lines.
Thanks, drew
Thanks
Care of "smp.cpus > 1" in the DT cpu-map part makes sense to me, because we are required to only add present cpu nodes to the DT and Linux Doc says that a cpu-map is not needed for uniprocessor systems.
Thanks, Yanan
acpi_add_table(table_offsets, tables_blob);build_pptt(tables_blob, tables->linker, vms);- }
acpi_add_table(table_offsets, tables_blob); build_gtdt(tables_blob, tables->linker, vms);
On 2021/5/18 15:17, Salil Mehta wrote:
From: Qemu-arm [mailto:qemu-arm-bounces+salil.mehta=huawei.com@nongnu.org] On Behalf Of wangyanan (Y) Sent: Thursday, May 13, 2021 6:10 AM
Hi Drew,
I got a question below, and hope your reply. Thanks! On 2021/4/13 16:07, Yanan Wang wrote:
Add the Processor Properties Topology Table (PPTT) to present CPU topology information to ACPI guests. Note, while a DT boot Linux guest with a non-flat CPU topology will see socket and core IDs being sequential integers starting from zero, e.g. with -smp 4,sockets=2,cores=2,threads=1
a DT boot produces
cpu: 0 package_id: 0 core_id: 0 cpu: 1 package_id: 0 core_id: 1 cpu: 2 package_id: 1 core_id: 0 cpu: 3 package_id: 1 core_id: 1
an ACPI boot produces
cpu: 0 package_id: 36 core_id: 0 cpu: 1 package_id: 36 core_id: 1 cpu: 2 package_id: 96 core_id: 2 cpu: 3 package_id: 96 core_id: 3
This is due to several reasons:
DT cpu nodes do not have an equivalent field to what the PPTT ACPI Processor ID must be, i.e. something equal to the MADT CPU UID or equal to the UID of an ACPI processor container. In both ACPI cases those are platform dependant IDs assigned by the vendor.
While QEMU is the vendor for a guest, if the topology specifies SMT (> 1 thread), then, with ACPI, it is impossible to assign a core-id the same value as a package-id, thus it is not possible to have package-id=0 and core-id=0. This is because package and core containers must be in the same ACPI namespace and therefore must have unique UIDs.
ACPI processor containers are not required for PPTT tables to be used and, due to the limitations of which IDs are selected described above in (2), they are not helpful for QEMU, so we don't build them with this patch. In the absence of them, Linux assigns its own unique IDs. The maintainers have chosen not to use counters from zero, but rather ACPI table offsets, which explains why the numbers are so much larger than with DT.
When there is no SMT (threads=1) the core IDs for ACPI boot guests match the logical CPU IDs, because these IDs must be equal to the MADT CPU UID (as no processor containers are present), and QEMU uses the logical CPU ID for these MADT IDs.
Tested-by: Jiajie Li lijiajie11@huawei.com Signed-off-by: Andrew Jones drjones@redhat.com Signed-off-by: Ying Fang fangying1@huawei.com Signed-off-by: Yanan Wang wangyanan55@huawei.com
hw/arm/virt-acpi-build.c | 63 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 63 insertions(+)
diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c index 2ad5dad1bf..03fd812d5a 100644 --- a/hw/arm/virt-acpi-build.c +++ b/hw/arm/virt-acpi-build.c @@ -436,6 +436,64 @@ build_srat(GArray *table_data, BIOSLinker *linker,
VirtMachineState *vms)
vms->oem_table_id);}
+/* PPTT */ +static void +build_pptt(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms) +{
- int pptt_start = table_data->len;
- int uid = 0, cpus = 0, socket = 0;
- MachineState *ms = MACHINE(vms);
- unsigned int smp_cores = ms->smp.cores;
- unsigned int smp_threads = ms->smp.threads;
- acpi_data_push(table_data, sizeof(AcpiTableHeader));
- for (socket = 0; cpus < ms->possible_cpus->len; socket++) {
uint32_t socket_offset = table_data->len - pptt_start;int core;build_processor_hierarchy_node(table_data, 1, /* Physical package */0, socket, /* No parent */NULL, 0); /* No private resources */for (core = 0; core < smp_cores; core++) {uint32_t core_offset = table_data->len - pptt_start;int thread;if (smp_threads <= 1) {build_processor_hierarchy_node(table_data,(1 << 1) | /* ACPI Processor ID valid */(1 << 3), /* ACPI 6.3 - Node is a Leaf */socket_offset, uid++, /* Parent is a Socket */NULL, 0); /* No private resources */} else {build_processor_hierarchy_node(table_data, 0,socket_offset, core, /* Parent is a Socket */NULL, 0); /* No private resources */for (thread = 0; thread < smp_threads; thread++) {build_processor_hierarchy_node(table_data,(1 << 1) | /* ACPI Processor ID valid */(1 << 2) | /* ACPI 6.3 - Processor is a Thread */(1 << 3), /* ACPI 6.3 - Node is a Leaf */core_offset, uid++, /* Parent is a Core */NULL, 0); /* No private resources */}}}cpus += smp_cores * smp_threads;- }
- build_header(linker, table_data,
(void *)(table_data->data + pptt_start), "PPTT",table_data->len - pptt_start, 2,vms->oem_id, vms->oem_table_id);+}
- /* GTDT */ static void build_gtdt(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms)
@@ -707,6 +765,11 @@ void virt_acpi_build(VirtMachineState *vms,
AcpiBuildTables *tables)
acpi_add_table(table_offsets, tables_blob); build_madt(tables_blob, tables->linker, vms);
- if (ms->smp.cpus > 1 && !vmc->no_cpu_topology) {
I'm not really sure why we need to care about "ms->smp.cpus > 1" here?
IMO, just like MADT in which we create both ENABLED and DISABLED gicc nodes no matter of number of ENABLED nodes is one or not, we should create PPTT table for all the possible cpus and not care about number of smp cpus, too. This will be more consistent with the ACPI specification and the PPTT table will be used for ACPI cpu hotplug in the future even with "smp.cpus == 1".
A humble request: Let us not anticipate the changes of vcpu Hotplug here. Things are fluid with respect to the vcpu Hotplug right now and I think it will not be right to base PPTT Table changes in anticipation of something we are not sure of what it looks like.
Hi Salil,
I agree with that I shouldn't anticipate vcpu hotplug which has little connect with this series. So it's not appropriately to consider too much of it when generating PPTT. I'm guessing this is what you mean.
Then PPTT generation is needed for cpu topology exposure to guest and the ACPI spec context also indicates that we should provided the hierarchy information of all cpus. See [1] (Note info at page 260). Can we agree on this ?
[1] https://uefi.org/sites/default/files/resources/ACPI_6_3_final_Jan30.pdf
Thanks, Yanan
Any such decisions should be postponed and be made part of the actual vcpu Hotplug changes when(and if ever) they come for ARM64. This will also ensure proper review of such changes and useful in that particular context.
Thanks
Care of "smp.cpus > 1" in the DT cpu-map part makes sense to me, because we are required to only add present cpu nodes to the DT and Linux Doc says that a cpu-map is not needed for uniprocessor systems.
Thanks, Yanan
acpi_add_table(table_offsets, tables_blob);build_pptt(tables_blob, tables->linker, vms);- }
acpi_add_table(table_offsets, tables_blob); build_gtdt(tables_blob, tables->linker, vms);
From: Andrew Jones [mailto:drjones@redhat.com] Sent: Tuesday, May 18, 2021 8:42 AM To: Salil Mehta salil.mehta@huawei.com Cc: wangyanan (Y) wangyanan55@huawei.com; Peter Maydell peter.maydell@linaro.org; Michael S . Tsirkin mst@redhat.com; Wanghaibin (D) wanghaibin.wang@huawei.com; qemu-devel@nongnu.org; Shannon Zhao shannon.zhaosl@gmail.com; qemu-arm@nongnu.org; Alistair Francis alistair.francis@wdc.com; Zengtao (B) prime.zeng@hisilicon.com; yangyicong yangyicong@huawei.com; yuzenghui yuzenghui@huawei.com; Igor Mammedov imammedo@redhat.com; zhukeqian zhukeqian1@huawei.com; lijiajie (H) lijiajie11@huawei.com; David Gibson david@gibson.dropbear.id.au; Linuxarm linuxarm@huawei.com; linuxarm@openeuler.org Subject: Re: [RFC PATCH v2 5/6] hw/arm/virt-acpi-build: Add PPTT table
On Tue, May 18, 2021 at 07:17:56AM +0000, Salil Mehta wrote:
From: Qemu-arm
[mailto:qemu-arm-bounces+salil.mehta=huawei.com@nongnu.org]
On Behalf Of wangyanan (Y) Sent: Thursday, May 13, 2021 6:10 AM
Hi Drew,
I got a question below, and hope your reply. Thanks! On 2021/4/13 16:07, Yanan Wang wrote:
Add the Processor Properties Topology Table (PPTT) to present CPU topology information to ACPI guests. Note, while a DT boot Linux guest with a non-flat CPU topology will see socket and core IDs being sequential integers starting from zero, e.g. with -smp 4,sockets=2,cores=2,threads=1
a DT boot produces
cpu: 0 package_id: 0 core_id: 0 cpu: 1 package_id: 0 core_id: 1 cpu: 2 package_id: 1 core_id: 0 cpu: 3 package_id: 1 core_id: 1
an ACPI boot produces
cpu: 0 package_id: 36 core_id: 0 cpu: 1 package_id: 36 core_id: 1 cpu: 2 package_id: 96 core_id: 2 cpu: 3 package_id: 96 core_id: 3
This is due to several reasons:
DT cpu nodes do not have an equivalent field to what the PPTT ACPI Processor ID must be, i.e. something equal to the MADT CPU UID or equal to the UID of an ACPI processor container. In both ACPI cases those are platform dependant IDs assigned by the vendor.
While QEMU is the vendor for a guest, if the topology specifies SMT (> 1 thread), then, with ACPI, it is impossible to assign a core-id the same value as a package-id, thus it is not possible to have package-id=0 and core-id=0. This is because package and core containers must be in the same ACPI namespace and therefore must have unique UIDs.
ACPI processor containers are not required for PPTT tables to be used and, due to the limitations of which IDs are selected described above in (2), they are not helpful for QEMU, so we don't build them with this patch. In the absence of them, Linux assigns its own unique IDs. The maintainers have chosen not to use counters from zero, but rather ACPI table offsets, which explains why the numbers are so much larger than with DT.
When there is no SMT (threads=1) the core IDs for ACPI boot guests match the logical CPU IDs, because these IDs must be equal to the MADT CPU UID (as no processor containers are present), and QEMU uses the logical CPU ID for these MADT IDs.
Tested-by: Jiajie Li lijiajie11@huawei.com Signed-off-by: Andrew Jones drjones@redhat.com Signed-off-by: Ying Fang fangying1@huawei.com Signed-off-by: Yanan Wang wangyanan55@huawei.com
hw/arm/virt-acpi-build.c | 63 ++++++++++++++++++++++++++++++++++++++++ 1 file changed, 63 insertions(+)
diff --git a/hw/arm/virt-acpi-build.c b/hw/arm/virt-acpi-build.c index 2ad5dad1bf..03fd812d5a 100644 --- a/hw/arm/virt-acpi-build.c +++ b/hw/arm/virt-acpi-build.c @@ -436,6 +436,64 @@ build_srat(GArray *table_data, BIOSLinker *linker,
VirtMachineState *vms)
vms->oem_table_id);}
+/* PPTT */ +static void +build_pptt(GArray *table_data, BIOSLinker *linker, VirtMachineState *vms) +{
- int pptt_start = table_data->len;
- int uid = 0, cpus = 0, socket = 0;
- MachineState *ms = MACHINE(vms);
- unsigned int smp_cores = ms->smp.cores;
- unsigned int smp_threads = ms->smp.threads;
- acpi_data_push(table_data, sizeof(AcpiTableHeader));
- for (socket = 0; cpus < ms->possible_cpus->len; socket++) {
uint32_t socket_offset = table_data->len - pptt_start;int core;build_processor_hierarchy_node(table_data, 1, /* Physical package */0, socket, /* No parent */NULL, 0); /* No private resources */for (core = 0; core < smp_cores; core++) {uint32_t core_offset = table_data->len - pptt_start;int thread;if (smp_threads <= 1) {build_processor_hierarchy_node(table_data,(1 << 1) | /* ACPI Processor ID valid */(1 << 3), /* ACPI 6.3 - Node is a Leaf */socket_offset, uid++, /* Parent is a Socket */NULL, 0); /* No private resources */} else {build_processor_hierarchy_node(table_data, 0,socket_offset, core, /* Parent is a Socket */NULL, 0); /* No private resources */for (thread = 0; thread < smp_threads; thread++) {build_processor_hierarchy_node(table_data,(1 << 1) | /* ACPI Processor ID valid */(1 << 2) | /* ACPI 6.3 - Processor is a Thread */(1 << 3), /* ACPI 6.3 - Node is a Leaf */core_offset, uid++, /* Parent is a Core */NULL, 0); /* No private resources */}}}cpus += smp_cores * smp_threads;- }
- build_header(linker, table_data,
(void *)(table_data->data + pptt_start), "PPTT",table_data->len - pptt_start, 2,vms->oem_id, vms->oem_table_id);+}
- /* GTDT */ static void build_gtdt(GArray *table_data, BIOSLinker *linker, VirtMachineState
*vms)
@@ -707,6 +765,11 @@ void virt_acpi_build(VirtMachineState *vms,
AcpiBuildTables *tables)
acpi_add_table(table_offsets, tables_blob); build_madt(tables_blob, tables->linker, vms);
- if (ms->smp.cpus > 1 && !vmc->no_cpu_topology) {
I'm not really sure why we need to care about "ms->smp.cpus > 1" here?
IMO, just like MADT in which we create both ENABLED and DISABLED gicc nodes no matter of number of ENABLED nodes is one or not, we should create PPTT table for all the possible cpus and not care about number of smp cpus, too. This will be more consistent with the ACPI specification and the PPTT table will be used for ACPI cpu hotplug in the future even with "smp.cpus == 1".
A humble request: Let us not anticipate the changes of vcpu Hotplug here. Things are fluid with respect to the vcpu Hotplug right now and I think it will not be right to base PPTT Table changes in anticipation of something we are not sure of what it looks like.
Any such decisions should be postponed and be made part of the actual vcpu Hotplug changes when(and if ever) they come for ARM64. This will also ensure proper review of such changes and useful in that particular context.
Hi Salil,
Can you please elaborate on this and send some pointers to the hot plug discussions?
Hi Andrew, As you are aware, ACPI based vcpu Hotplug is under contention right now. It is being discussed within the ARM to have Hotplug mechanism which does not involves QEMU<->Guest ACPI Hotplug exchanges and are purely based on PSCI triggers(which might take a different ACPI path). If you wish you can join Linaro Open Discussion meeting for the same. All these discussions have been happening there
https://linaro.atlassian.net/wiki/spaces/LOD/pages/26844463630/2021-5-25+Mee...
You're not saying that we shouldn't try to generate PPTT
tables for AArch64 guests until a solution for hot plug has been determined, are you?
Sorry, I did not mean that. Changes of PPTT are independent to vcpu Hotplug support and are still required without it. No problem with that.
If so, I don't think I would agree with that. There
are benefits to properly describing cpu topology to guests, even without hot plug.
Agreed. No second thoughts on that.
Those benefits, when vcpu pinning is used, are the same benefits
as for the host, which already use PPTT tables to describe topology, even though hot plug isn't supported.
yes sure, you mean pinning vcpus according to the cpu topology for performance?
Now, if you're saying we should only generate tables for smp.cpus, not
Correct. This is what I thought we must be doing even now
smp.maxcpus, because hot plug isn't supported anyway, then I see your point. But, it'd be better to require smp.cpus == smp.maxcpus in our smp_parse function to do that, which we've never done before, so we may have trouble supporting existing command lines.
I am trying to recall, if the vcpu Hotplug is not supported then can they ever be different?
cpus = (threads * cores * sockets)
static void smp_parse(MachineState *ms, QemuOpts *opts) { [...]
if (sockets * cores * threads != ms->smp.max_cpus) { warn_report("Invalid CPU topology deprecated: " "sockets (%u) * cores (%u) * threads (%u) " "!= maxcpus (%u)", sockets, cores, threads, ms->smp.max_cpus); } [...] }
Although, above check does not exit(1) and just warns on detecting invalid CPU topology. Not sure why?
Well if you think there are subtleties to support above implementation and we cannot do it now then sure it is your call. :)
I just thought to slim the patch-set down and club the relevant logic to the places where they ideally would have made more sense to review.
Thanks Salil.
On Tue, May 18, 2021 at 06:34:08PM +0000, Salil Mehta wrote:
Those benefits, when vcpu pinning is used, are the same benefits
as for the host, which already use PPTT tables to describe topology, even though hot plug isn't supported.
yes sure, you mean pinning vcpus according to the cpu topology for performance?
Yup
Now, if you're saying we should only generate tables for smp.cpus, not
Correct. This is what I thought we must be doing even now
smp.maxcpus, because hot plug isn't supported anyway, then I see your point. But, it'd be better to require smp.cpus == smp.maxcpus in our smp_parse function to do that, which we've never done before, so we may have trouble supporting existing command lines.
I am trying to recall, if the vcpu Hotplug is not supported then can they ever be different?
cpus = (threads * cores * sockets)
static void smp_parse(MachineState *ms, QemuOpts *opts) { [...]
if (sockets * cores * threads != ms->smp.max_cpus) { warn_report("Invalid CPU topology deprecated: " "sockets (%u) * cores (%u) * threads (%u) " "!= maxcpus (%u)", sockets, cores, threads, ms->smp.max_cpus); } [...]}
Although, above check does not exit(1) and just warns on detecting invalid CPU topology. Not sure why?
Hmm, not sure what code you have there. I see this in hw/core/machine.c:smp_parse
if (ms->smp.max_cpus < cpus) { error_report("maxcpus must be equal to or greater than smp"); exit(1); }
if (sockets * cores * threads != ms->smp.max_cpus) { error_report("Invalid CPU topology: " "sockets (%u) * cores (%u) * threads (%u) " "!= maxcpus (%u)", sockets, cores, threads, ms->smp.max_cpus); exit(1); }
Well if you think there are subtleties to support above implementation and we cannot do it now then sure it is your call. :)
The problem is that -smp 4,maxcpus=8 doesn't error out today, even though it doesn't do anything. OTOH, -smp 4,cores=2 doesn't error out either, but we're proposing that it should. Maybe we can start erroring out when cpus != maxcpus until hot plug is supported?
Thanks, drew
From: Andrew Jones [mailto:drjones@redhat.com] Sent: Tuesday, May 18, 2021 8:06 PM To: Salil Mehta salil.mehta@huawei.com Cc: wangyanan (Y) wangyanan55@huawei.com; Peter Maydell peter.maydell@linaro.org; Michael S . Tsirkin mst@redhat.com; Wanghaibin (D) wanghaibin.wang@huawei.com; qemu-devel@nongnu.org; Shannon Zhao shannon.zhaosl@gmail.com; qemu-arm@nongnu.org; Alistair Francis alistair.francis@wdc.com; Zengtao (B) prime.zeng@hisilicon.com; yangyicong yangyicong@huawei.com; yuzenghui yuzenghui@huawei.com; Igor Mammedov imammedo@redhat.com; zhukeqian zhukeqian1@huawei.com; lijiajie (H) lijiajie11@huawei.com; David Gibson david@gibson.dropbear.id.au; Linuxarm linuxarm@huawei.com; linuxarm@openeuler.org Subject: Re: [RFC PATCH v2 5/6] hw/arm/virt-acpi-build: Add PPTT table
On Tue, May 18, 2021 at 06:34:08PM +0000, Salil Mehta wrote:
Those benefits, when vcpu pinning is used, are the same benefits
as for the host, which already use PPTT tables to describe topology, even though hot plug isn't supported.
yes sure, you mean pinning vcpus according to the cpu topology for performance?
Yup
Already Agreed :)
Now, if you're saying we should only generate tables for smp.cpus, not
Correct. This is what I thought we must be doing even now
smp.maxcpus, because hot plug isn't supported anyway, then I see your point. But, it'd be better to require smp.cpus == smp.maxcpus in our smp_parse function to do that, which we've never done before, so we may have trouble supporting existing command lines.
I am trying to recall, if the vcpu Hotplug is not supported then can they ever be different?
cpus = (threads * cores * sockets)
static void smp_parse(MachineState *ms, QemuOpts *opts) { [...]
if (sockets * cores * threads != ms->smp.max_cpus) { warn_report("Invalid CPU topology deprecated: " "sockets (%u) * cores (%u) * threads (%u) " "!= maxcpus (%u)", sockets, cores, threads, ms->smp.max_cpus); } [...]}
Although, above check does not exit(1) and just warns on detecting invalid CPU topology. Not sure why?
Hmm, not sure what code you have there. I see this in hw/core/machine.c:smp_parse
if (ms->smp.max_cpus < cpus) { error_report("maxcpus must be equal to or greater than smp"); exit(1); } if (sockets * cores * threads != ms->smp.max_cpus) { error_report("Invalid CPU topology: " "sockets (%u) * cores (%u) * threads (%u) " "!= maxcpus (%u)", sockets, cores, threads, ms->smp.max_cpus); exit(1); }Well if you think there are subtleties to support above implementation and we cannot do it now then sure it is your call. :)
The problem is that -smp 4,maxcpus=8 doesn't error out today, even though it doesn't do anything. OTOH, -smp 4,cores=2 doesn't error out either, but we're proposing that it should. Maybe we can start erroring out when cpus != maxcpus until hot plug is supported?
Agreed, both don't make any sense if hotplug is not supported and ideally should fail with error. We should block any such topology configuration.
Thanks Salil
On 2021/5/19 3:22, Salil Mehta wrote:
From: Andrew Jones [mailto:drjones@redhat.com] Sent: Tuesday, May 18, 2021 8:06 PM To: Salil Mehta salil.mehta@huawei.com Cc: wangyanan (Y) wangyanan55@huawei.com; Peter Maydell peter.maydell@linaro.org; Michael S . Tsirkin mst@redhat.com; Wanghaibin (D) wanghaibin.wang@huawei.com; qemu-devel@nongnu.org; Shannon Zhao shannon.zhaosl@gmail.com; qemu-arm@nongnu.org; Alistair Francis alistair.francis@wdc.com; Zengtao (B) prime.zeng@hisilicon.com; yangyicong yangyicong@huawei.com; yuzenghui yuzenghui@huawei.com; Igor Mammedov imammedo@redhat.com; zhukeqian zhukeqian1@huawei.com; lijiajie (H) lijiajie11@huawei.com; David Gibson david@gibson.dropbear.id.au; Linuxarm linuxarm@huawei.com; linuxarm@openeuler.org Subject: Re: [RFC PATCH v2 5/6] hw/arm/virt-acpi-build: Add PPTT table
On Tue, May 18, 2021 at 06:34:08PM +0000, Salil Mehta wrote:
Those benefits, when vcpu pinning is used, are the same benefits
as for the host, which already use PPTT tables to describe topology, even though hot plug isn't supported.
yes sure, you mean pinning vcpus according to the cpu topology for performance?
Yup
Already Agreed :)
Now, if you're saying we should only generate tables for smp.cpus, not
Correct. This is what I thought we must be doing even now
smp.maxcpus, because hot plug isn't supported anyway, then I see your point. But, it'd be better to require smp.cpus == smp.maxcpus in our smp_parse function to do that, which we've never done before, so we may have trouble supporting existing command lines.
I am trying to recall, if the vcpu Hotplug is not supported then can they ever be different?
cpus = (threads * cores * sockets)
static void smp_parse(MachineState *ms, QemuOpts *opts) { [...]
if (sockets * cores * threads != ms->smp.max_cpus) { warn_report("Invalid CPU topology deprecated: " "sockets (%u) * cores (%u) * threads (%u) " "!= maxcpus (%u)", sockets, cores, threads, ms->smp.max_cpus); } [...]}
Although, above check does not exit(1) and just warns on detecting invalid CPU topology. Not sure why?
Hmm, not sure what code you have there. I see this in hw/core/machine.c:smp_parse
if (ms->smp.max_cpus < cpus) { error_report("maxcpus must be equal to or greater than smp"); exit(1); } if (sockets * cores * threads != ms->smp.max_cpus) { error_report("Invalid CPU topology: " "sockets (%u) * cores (%u) * threads (%u) " "!= maxcpus (%u)", sockets, cores, threads, ms->smp.max_cpus); exit(1); }Well if you think there are subtleties to support above implementation and we cannot do it now then sure it is your call. :)
Hi Salil, Drew,
The problem is that -smp 4,maxcpus=8 doesn't error out today, even though it doesn't do anything. OTOH, -smp 4,cores=2 doesn't error out either, but we're proposing that it should. Maybe we can start erroring out when cpus != maxcpus until hot plug is supported?
Agreed, both don't make any sense if hotplug is not supported and ideally should fail with error. We should block any such topology configuration.
In the ARM-specific function virt_smp_parse() (patch 9), there already have been some restrictions for the given -smp configuration. We now only allow: -smp N -smp maxcpus=M -smp N, maxcpus=M
-smp N, sockets=X, cores=Y -smp N, sockets=X, cores=Y, threads=Z
-smp maxcpus=M, sockets=X, cores=Y -smp maxcpus=M, sockets=X, cores=Y, threads=Z
-smp N, maxcpus=M, sockets=X, cores=Y -smp N, maxcpus=M, sockets=X, cores=Y, threads=Z
and disallow the other strange and rare formats that shouldn't be provided.
It's reasonable to block the topology configuration which is not useful currently. I will add the requirement for "cpus==maxcpus" in this fuction if the possible conflict with existing command lines is not a big problem.
Thanks, Yanan
Thanks Salil .
From: wangyanan (Y) Sent: Wednesday, May 19, 2021 4:18 AM
On 2021/5/19 3:22, Salil Mehta wrote:
From: Andrew Jones [mailto:drjones@redhat.com] Sent: Tuesday, May 18, 2021 8:06 PM To: Salil Mehta salil.mehta@huawei.com Cc: wangyanan (Y) wangyanan55@huawei.com; Peter Maydell peter.maydell@linaro.org; Michael S . Tsirkin mst@redhat.com; Wanghaibin (D) wanghaibin.wang@huawei.com; qemu-devel@nongnu.org; Shannon Zhao shannon.zhaosl@gmail.com; qemu-arm@nongnu.org; Alistair Francis alistair.francis@wdc.com; Zengtao (B) prime.zeng@hisilicon.com; yangyicong yangyicong@huawei.com; yuzenghui yuzenghui@huawei.com; Igor Mammedov imammedo@redhat.com; zhukeqian zhukeqian1@huawei.com; lijiajie
(H)
lijiajie11@huawei.com; David Gibson david@gibson.dropbear.id.au;
Linuxarm
linuxarm@huawei.com; linuxarm@openeuler.org Subject: Re: [RFC PATCH v2 5/6] hw/arm/virt-acpi-build: Add PPTT table
On Tue, May 18, 2021 at 06:34:08PM +0000, Salil Mehta wrote:
Those benefits, when vcpu pinning is used, are the same benefits
as for the host, which already use PPTT tables to describe topology, even though hot plug isn't supported.
yes sure, you mean pinning vcpus according to the cpu topology for performance?
Yup
Already Agreed :)
Now, if you're saying we should only generate tables for smp.cpus, not
Correct. This is what I thought we must be doing even now
smp.maxcpus, because hot plug isn't supported anyway, then I see your point. But, it'd be better to require smp.cpus == smp.maxcpus in our smp_parse function to do that, which we've never done before, so we may have trouble supporting existing command lines.
I am trying to recall, if the vcpu Hotplug is not supported then can they ever be different?
cpus = (threads * cores * sockets)
static void smp_parse(MachineState *ms, QemuOpts *opts) { [...]
if (sockets * cores * threads != ms->smp.max_cpus) { warn_report("Invalid CPU topology deprecated: " "sockets (%u) * cores (%u) * threads (%u) " "!= maxcpus (%u)", sockets, cores, threads, ms->smp.max_cpus); } [...]}
Although, above check does not exit(1) and just warns on detecting invalid CPU topology. Not sure why?
Hmm, not sure what code you have there. I see this in hw/core/machine.c:smp_parse
if (ms->smp.max_cpus < cpus) { error_report("maxcpus must be equal to or greater than smp"); exit(1); } if (sockets * cores * threads != ms->smp.max_cpus) { error_report("Invalid CPU topology: " "sockets (%u) * cores (%u) * threads (%u) " "!= maxcpus (%u)", sockets, cores, threads, ms->smp.max_cpus); exit(1); }Well if you think there are subtleties to support above implementation and we cannot do it now then sure it is your call. :)
Hi Salil, Drew,
The problem is that -smp 4,maxcpus=8 doesn't error out today, even though it doesn't do anything. OTOH, -smp 4,cores=2 doesn't error out either, but we're proposing that it should. Maybe we can start erroring out when cpus != maxcpus until hot plug is supported?
Agreed, both don't make any sense if hotplug is not supported and ideally should fail with error. We should block any such topology configuration.
In the ARM-specific function virt_smp_parse() (patch 9), there already have been some restrictions for the given -smp configuration. We now only allow: -smp N -smp maxcpus=M -smp N, maxcpus=M
-smp N, sockets=X, cores=Y -smp N, sockets=X, cores=Y, threads=Z
-smp maxcpus=M, sockets=X, cores=Y -smp maxcpus=M, sockets=X, cores=Y, threads=Z
-smp N, maxcpus=M, sockets=X, cores=Y -smp N, maxcpus=M, sockets=X, cores=Y, threads=Z
and disallow the other strange and rare formats that shouldn't be provided.
It's reasonable to block the topology configuration which is not useful currently. I will add the requirement for "cpus==maxcpus" in this fuction if the possible conflict with existing command lines is not a big problem.
Hi Yanan, Makes sense. I did see your other patch-set in which cluster support has been added. Are we deferring that too?
Thanks
On Wed, May 19, 2021 at 07:54:37AM +0000, Salil Mehta wrote:
From: wangyanan (Y) Sent: Wednesday, May 19, 2021 4:18 AM
On 2021/5/19 3:22, Salil Mehta wrote:
From: Andrew Jones [mailto:drjones@redhat.com] Sent: Tuesday, May 18, 2021 8:06 PM To: Salil Mehta salil.mehta@huawei.com Cc: wangyanan (Y) wangyanan55@huawei.com; Peter Maydell peter.maydell@linaro.org; Michael S . Tsirkin mst@redhat.com; Wanghaibin (D) wanghaibin.wang@huawei.com; qemu-devel@nongnu.org; Shannon Zhao shannon.zhaosl@gmail.com; qemu-arm@nongnu.org; Alistair Francis alistair.francis@wdc.com; Zengtao (B) prime.zeng@hisilicon.com; yangyicong yangyicong@huawei.com; yuzenghui yuzenghui@huawei.com; Igor Mammedov imammedo@redhat.com; zhukeqian zhukeqian1@huawei.com; lijiajie
(H)
lijiajie11@huawei.com; David Gibson david@gibson.dropbear.id.au;
Linuxarm
linuxarm@huawei.com; linuxarm@openeuler.org Subject: Re: [RFC PATCH v2 5/6] hw/arm/virt-acpi-build: Add PPTT table
On Tue, May 18, 2021 at 06:34:08PM +0000, Salil Mehta wrote:
Those benefits, when vcpu pinning is used, are the same benefits
as for the host, which already use PPTT tables to describe topology, even though hot plug isn't supported.
yes sure, you mean pinning vcpus according to the cpu topology for performance?
Yup
Already Agreed :)
Now, if you're saying we should only generate tables for smp.cpus, not
Correct. This is what I thought we must be doing even now
smp.maxcpus, because hot plug isn't supported anyway, then I see your point. But, it'd be better to require smp.cpus == smp.maxcpus in our smp_parse function to do that, which we've never done before, so we may have trouble supporting existing command lines.
I am trying to recall, if the vcpu Hotplug is not supported then can they ever be different?
cpus = (threads * cores * sockets)
static void smp_parse(MachineState *ms, QemuOpts *opts) { [...]
if (sockets * cores * threads != ms->smp.max_cpus) { warn_report("Invalid CPU topology deprecated: " "sockets (%u) * cores (%u) * threads (%u) " "!= maxcpus (%u)", sockets, cores, threads, ms->smp.max_cpus); } [...]}
Although, above check does not exit(1) and just warns on detecting invalid CPU topology. Not sure why?
Hmm, not sure what code you have there. I see this in hw/core/machine.c:smp_parse
if (ms->smp.max_cpus < cpus) { error_report("maxcpus must be equal to or greater than smp"); exit(1); } if (sockets * cores * threads != ms->smp.max_cpus) { error_report("Invalid CPU topology: " "sockets (%u) * cores (%u) * threads (%u) " "!= maxcpus (%u)", sockets, cores, threads, ms->smp.max_cpus); exit(1); }Well if you think there are subtleties to support above implementation and we cannot do it now then sure it is your call. :)
Hi Salil, Drew,
The problem is that -smp 4,maxcpus=8 doesn't error out today, even though it doesn't do anything. OTOH, -smp 4,cores=2 doesn't error out either, but we're proposing that it should. Maybe we can start erroring out when cpus != maxcpus until hot plug is supported?
Agreed, both don't make any sense if hotplug is not supported and ideally should fail with error. We should block any such topology configuration.
In the ARM-specific function virt_smp_parse() (patch 9), there already have been some restrictions for the given -smp configuration. We now only allow: -smp N -smp maxcpus=M -smp N, maxcpus=M
-smp N, sockets=X, cores=Y -smp N, sockets=X, cores=Y, threads=Z
-smp maxcpus=M, sockets=X, cores=Y -smp maxcpus=M, sockets=X, cores=Y, threads=Z
-smp N, maxcpus=M, sockets=X, cores=Y -smp N, maxcpus=M, sockets=X, cores=Y, threads=Z
and disallow the other strange and rare formats that shouldn't be provided.
It's reasonable to block the topology configuration which is not useful currently. I will add the requirement for "cpus==maxcpus" in this fuction if the possible conflict with existing command lines is not a big problem.
Hi Yanan, Makes sense. I did see your other patch-set in which cluster support has been added. Are we deferring that too?
The merge of that needs to be deferred, but for a different reason. It shouldn't impact hot plug, because if hot plug doesn't like clusters, then one could configure a topology which doesn't have clusters. But, it can't be merged to QEMU until the kernel has merged its support.
Thanks, drew
On Tue, May 18, 2021 at 09:05:39PM +0200, Andrew Jones wrote:
The problem is that -smp 4,maxcpus=8 doesn't error out today, even though it doesn't do anything. OTOH, -smp 4,cores=2 doesn't error out either, but we're proposing that it should. Maybe we can start erroring out when cpus != maxcpus until hot plug is supported?
The more I think about this, the more I think we're in a bit of pickle and need Peter Maydell to chime in. While we may want to make our -smp command line option parsing more strict in order to bring some sanity to it, if we do, then we'll break existing command lines, which, while may be specifying useless inputs, have always gotten away with it. We probably can't just change that now without forcing the user to opt into it. Maybe we need to add another -smp parameter like 'strict' that has to be set to 'on' in order to get this new behavior.
Peter, do you have some suggestions for this? A summary of the problem we'd like to solve is as follows:
We'd like to start describing CPU topology to guests when provided topology information with the '-smp ...' command line option. Currently, a user may provide nearly whatever it wants on that command line option and not get an error, even though the guest will not get a topology description. When building the topology its important to know what the user actually wants, so we're proposing to require both sockets and cores be given if one of them is given. Also, since we don't yet support hot plug for AArch64, we're proposing to enforce cpus == maxcpus.
Is it fine to make those changes to the parsing for 6.1 and later? (Note, mach-virt will override the default smp_parse with its own, so this is mach-virt specific.) Or, should we only do this if a new parameter is also given, e.g. 'strict'. Something like
-smp strict=on,cpus=4,sockets=2,cores=2
would be needed by users who want to describe cpu topologies. Without a strict description, then they get what they get today for their DT/ACPI topology description, nothing.
Thanks, drew
On 2021/5/19 16:15, Andrew Jones wrote:
On Wed, May 19, 2021 at 07:54:37AM +0000, Salil Mehta wrote:
From: wangyanan (Y) Sent: Wednesday, May 19, 2021 4:18 AM
On 2021/5/19 3:22, Salil Mehta wrote:
From: Andrew Jones [mailto:drjones@redhat.com] Sent: Tuesday, May 18, 2021 8:06 PM To: Salil Mehta salil.mehta@huawei.com Cc: wangyanan (Y) wangyanan55@huawei.com; Peter Maydell peter.maydell@linaro.org; Michael S . Tsirkin mst@redhat.com; Wanghaibin (D) wanghaibin.wang@huawei.com; qemu-devel@nongnu.org; Shannon Zhao shannon.zhaosl@gmail.com; qemu-arm@nongnu.org; Alistair Francis alistair.francis@wdc.com; Zengtao (B) prime.zeng@hisilicon.com; yangyicong yangyicong@huawei.com; yuzenghui yuzenghui@huawei.com; Igor Mammedov imammedo@redhat.com; zhukeqian zhukeqian1@huawei.com; lijiajie
(H)
lijiajie11@huawei.com; David Gibson david@gibson.dropbear.id.au;
Linuxarm
linuxarm@huawei.com; linuxarm@openeuler.org Subject: Re: [RFC PATCH v2 5/6] hw/arm/virt-acpi-build: Add PPTT table
On Tue, May 18, 2021 at 06:34:08PM +0000, Salil Mehta wrote:
Those benefits, when vcpu pinning is used, are the same benefits > as for the host, which already use PPTT tables to describe topology, even > though hot plug isn't supported. yes sure, you mean pinning vcpus according to the cpu topology for performance?
Yup
Already Agreed :)
> Now, if you're saying we should only generate tables for smp.cpus, not Correct. This is what I thought we must be doing even now
> smp.maxcpus, because hot plug isn't supported anyway, then I see your > point. But, it'd be better to require smp.cpus == smp.maxcpus in our > smp_parse function to do that, which we've never done before, so we may > have trouble supporting existing command lines. I am trying to recall, if the vcpu Hotplug is not supported then can they ever be different?
cpus = (threads * cores * sockets)
static void smp_parse(MachineState *ms, QemuOpts *opts) { [...]
if (sockets * cores * threads != ms->smp.max_cpus) { warn_report("Invalid CPU topology deprecated: " "sockets (%u) * cores (%u) * threads (%u) " "!= maxcpus (%u)", sockets, cores, threads, ms->smp.max_cpus); } [...]}
Although, above check does not exit(1) and just warns on detecting invalid CPU topology. Not sure why?
Hmm, not sure what code you have there. I see this in hw/core/machine.c:smp_parse
if (ms->smp.max_cpus < cpus) { error_report("maxcpus must be equal to or greater than smp"); exit(1); } if (sockets * cores * threads != ms->smp.max_cpus) { error_report("Invalid CPU topology: " "sockets (%u) * cores (%u) * threads (%u) " "!= maxcpus (%u)", sockets, cores, threads, ms->smp.max_cpus); exit(1); }Well if you think there are subtleties to support above implementation and we cannot do it now then sure it is your call. :)
Hi Salil, Drew,
The problem is that -smp 4,maxcpus=8 doesn't error out today, even though it doesn't do anything. OTOH, -smp 4,cores=2 doesn't error out either, but we're proposing that it should. Maybe we can start erroring out when cpus != maxcpus until hot plug is supported?
Agreed, both don't make any sense if hotplug is not supported and ideally should fail with error. We should block any such topology configuration.
In the ARM-specific function virt_smp_parse() (patch 9), there already have been some restrictions for the given -smp configuration. We now only allow: -smp N -smp maxcpus=M -smp N, maxcpus=M
-smp N, sockets=X, cores=Y -smp N, sockets=X, cores=Y, threads=Z
-smp maxcpus=M, sockets=X, cores=Y -smp maxcpus=M, sockets=X, cores=Y, threads=Z
-smp N, maxcpus=M, sockets=X, cores=Y -smp N, maxcpus=M, sockets=X, cores=Y, threads=Z
and disallow the other strange and rare formats that shouldn't be provided.
It's reasonable to block the topology configuration which is not useful currently. I will add the requirement for "cpus==maxcpus" in this fuction if the possible conflict with existing command lines is not a big problem.
Hi Yanan, Makes sense. I did see your other patch-set in which cluster support has been added. Are we deferring that too?
The merge of that needs to be deferred, but for a different reason. It shouldn't impact hot plug, because if hot plug doesn't like clusters, then one could configure a topology which doesn't have clusters. But, it can't be merged to QEMU until the kernel has merged its support.
Agreed!
Thanks, Yanan
Thanks, drew
.
From: Andrew Jones [mailto:drjones@redhat.com] Sent: Wednesday, May 19, 2021 9:15 AM
On Wed, May 19, 2021 at 07:54:37AM +0000, Salil Mehta wrote:
From: wangyanan (Y) Sent: Wednesday, May 19, 2021 4:18 AM
On 2021/5/19 3:22, Salil Mehta wrote:
From: Andrew Jones [mailto:drjones@redhat.com] Sent: Tuesday, May 18, 2021 8:06 PM To: Salil Mehta salil.mehta@huawei.com Cc: wangyanan (Y) wangyanan55@huawei.com; Peter Maydell peter.maydell@linaro.org; Michael S . Tsirkin mst@redhat.com; Wanghaibin (D) wanghaibin.wang@huawei.com; qemu-devel@nongnu.org; Shannon Zhao shannon.zhaosl@gmail.com; qemu-arm@nongnu.org; Alistair Francis alistair.francis@wdc.com; Zengtao (B) prime.zeng@hisilicon.com; yangyicong yangyicong@huawei.com; yuzenghui yuzenghui@huawei.com; Igor Mammedov imammedo@redhat.com; zhukeqian zhukeqian1@huawei.com; lijiajie (H) lijiajie11@huawei.com; David Gibson david@gibson.dropbear.id.au; Linuxarm linuxarm@huawei.com; linuxarm@openeuler.org Subject: Re: [RFC PATCH v2 5/6] hw/arm/virt-acpi-build: Add PPTT table
On Tue, May 18, 2021 at 06:34:08PM +0000, Salil Mehta wrote:
Those benefits, when vcpu pinning is used, are the same benefits > as for the host, which already use PPTT tables to describe topology, even > though hot plug isn't supported. yes sure, you mean pinning vcpus according to the cpu topology for performance?
Yup
Already Agreed :)
> Now, if you're saying we should only generate tables for smp.cpus, not Correct. This is what I thought we must be doing even now
> smp.maxcpus, because hot plug isn't supported anyway, then I see your > point. But, it'd be better to require smp.cpus == smp.maxcpus in our > smp_parse function to do that, which we've never done before, so we may > have trouble supporting existing command lines. I am trying to recall, if the vcpu Hotplug is not supported then can they ever be different?
cpus = (threads * cores * sockets)
static void smp_parse(MachineState *ms, QemuOpts *opts) { [...]
if (sockets * cores * threads != ms->smp.max_cpus) { warn_report("Invalid CPU topology deprecated: " "sockets (%u) * cores (%u) * threads (%u) " "!= maxcpus (%u)", sockets, cores, threads, ms->smp.max_cpus); } [...]}
Although, above check does not exit(1) and just warns on detecting invalid CPU topology. Not sure why?
Hmm, not sure what code you have there. I see this in hw/core/machine.c:smp_parse
if (ms->smp.max_cpus < cpus) { error_report("maxcpus must be equal to or greater than smp"); exit(1); } if (sockets * cores * threads != ms->smp.max_cpus) { error_report("Invalid CPU topology: " "sockets (%u) * cores (%u) * threads (%u) " "!= maxcpus (%u)", sockets, cores, threads, ms->smp.max_cpus); exit(1); }Well if you think there are subtleties to support above implementation and we cannot do it now then sure it is your call. :)
Hi Salil, Drew,
The problem is that -smp 4,maxcpus=8 doesn't error out today, even though it doesn't do anything. OTOH, -smp 4,cores=2 doesn't error out either, but we're proposing that it should. Maybe we can start erroring out when cpus != maxcpus until hot plug is supported?
Agreed, both don't make any sense if hotplug is not supported and ideally should fail with error. We should block any such topology configuration.
In the ARM-specific function virt_smp_parse() (patch 9), there already have been some restrictions for the given -smp configuration. We now only allow: -smp N -smp maxcpus=M -smp N, maxcpus=M
-smp N, sockets=X, cores=Y -smp N, sockets=X, cores=Y, threads=Z
-smp maxcpus=M, sockets=X, cores=Y -smp maxcpus=M, sockets=X, cores=Y, threads=Z
-smp N, maxcpus=M, sockets=X, cores=Y -smp N, maxcpus=M, sockets=X, cores=Y, threads=Z
and disallow the other strange and rare formats that shouldn't be provided.
It's reasonable to block the topology configuration which is not useful currently. I will add the requirement for "cpus==maxcpus" in this fuction if the possible conflict with existing command lines is not a big problem.
Hi Yanan, Makes sense. I did see your other patch-set in which cluster support has been added. Are we deferring that too?
The merge of that needs to be deferred, but for a different reason. It shouldn't impact hot plug, because if hot plug doesn't like clusters, then one could configure a topology which doesn't have clusters. But,
yes, agreed.
it can't be merged to QEMU until the kernel has merged its support.
sure.
Hi Drew,
On 2021/5/19 16:27, Andrew Jones wrote:
On Tue, May 18, 2021 at 09:05:39PM +0200, Andrew Jones wrote:
The problem is that -smp 4,maxcpus=8 doesn't error out today, even though it doesn't do anything. OTOH, -smp 4,cores=2 doesn't error out either, but we're proposing that it should. Maybe we can start erroring out when cpus != maxcpus until hot plug is supported?
The more I think about this, the more I think we're in a bit of pickle and need Peter Maydell to chime in. While we may want to make our -smp command line option parsing more strict in order to bring some sanity to it, if we do, then we'll break existing command lines, which, while may be specifying useless inputs, have always gotten away with it. We probably can't just change that now without forcing the user to opt into it. Maybe we need to add another -smp parameter like 'strict' that has to be set to 'on' in order to get this new behavior.
Peter, do you have some suggestions for this? A summary of the problem we'd like to solve is as follows:
We'd like to start describing CPU topology to guests when provided topology information with the '-smp ...' command line option. Currently, a user may provide nearly whatever it wants on that command line option and not get an error, even though the guest will not get a topology description. When building the topology its important to know what the user actually wants, so we're proposing to require both sockets and cores be given if one of them is given. Also, since we don't yet support hot plug for AArch64, we're proposing to enforce cpus == maxcpus.
Is it fine to make those changes to the parsing for 6.1 and later? (Note, mach-virt will override the default smp_parse with its own, so this is mach-virt specific.) Or, should we only do this if a new parameter is also given, e.g. 'strict'. Something like
-smp strict=on,cpus=4,sockets=2,cores=2
would be needed by users who want to describe cpu topologies. Without a strict description, then they get what they get today for their DT/ACPI topology description, nothing.
From my point of view, I like the idea of a new parameter like "strict=on/off". I will explain the reason below but maybe I have missed something, so I also hope for some suggestions from Peter. :)
1) We don't need to worry about breaking any existing -smp command lines including the rare and strange ones any more, since we will only have more strict requirement for the new provided cmdlines with "strict=on" and only generate topology description to guest with these new cmdlines provided.
2) This will provide an option for users to decide whether to enable the feature or not. Furthermore, this feature can also work on older machine types, if a user want to make use of cpu topology exposure to guest on older machines and is also sure it won't affect the application's behavior, then he can read the Doc and properly provided a -smp cmdline with "strict=on" to boot a VM.
3) We don't need to bother guessing different formats of -smp command lines in parsing. If the new parameter is not specified or "strict=off" is provided, we totally follow the rules in smp_parse() and disable the topology exposure. And if "strict=on" is provided, we enable the topology exposure and enforce completely detailed configuration like "-smp strict=on,cpus=4,sockets=2,cores=2".
But maxcpus will be optional, it will default to cpus if not provided. We also ensure it matches cpus if provided, given that cpu hotplug is not available yet.
Thanks, Yanan
Thanks, drew
.
On 2021/5/19 21:26, wangyanan (Y) wrote:
Hi Drew,
On 2021/5/19 16:27, Andrew Jones wrote:
On Tue, May 18, 2021 at 09:05:39PM +0200, Andrew Jones wrote:
The problem is that -smp 4,maxcpus=8 doesn't error out today, even though it doesn't do anything. OTOH, -smp 4,cores=2 doesn't error out either, but we're proposing that it should. Maybe we can start erroring out when cpus != maxcpus until hot plug is supported?
The more I think about this, the more I think we're in a bit of pickle and need Peter Maydell to chime in. While we may want to make our -smp command line option parsing more strict in order to bring some sanity to it, if we do, then we'll break existing command lines, which, while may be specifying useless inputs, have always gotten away with it. We probably can't just change that now without forcing the user to opt into it. Maybe we need to add another -smp parameter like 'strict' that has to be set to 'on' in order to get this new behavior.
Peter, do you have some suggestions for this? A summary of the problem we'd like to solve is as follows:
We'd like to start describing CPU topology to guests when provided topology information with the '-smp ...' command line option. Currently, a user may provide nearly whatever it wants on that command line option and not get an error, even though the guest will not get a topology description. When building the topology its important to know what the user actually wants, so we're proposing to require both sockets and cores be given if one of them is given. Also, since we don't yet support hot plug for AArch64, we're proposing to enforce cpus == maxcpus.
Is it fine to make those changes to the parsing for 6.1 and later? (Note, mach-virt will override the default smp_parse with its own, so this is mach-virt specific.) Or, should we only do this if a new parameter is also given, e.g. 'strict'. Something like
-smp strict=on,cpus=4,sockets=2,cores=2
would be needed by users who want to describe cpu topologies. Without a strict description, then they get what they get today for their DT/ACPI topology description, nothing.
From my point of view, I like the idea of a new parameter like "strict=on/off". I will explain the reason below but maybe I have missed something, so I also hope for some suggestions from Peter. :)
- We don't need to worry about breaking any existing -smp command lines
including the rare and strange ones any more, since we will only have more strict requirement for the new provided cmdlines with "strict=on" and only generate topology description to guest with these new cmdlines provided.
- This will provide an option for users to decide whether to enable
the feature or not. Furthermore, this feature can also work on older machine types, if a user want to make use of cpu topology exposure to guest on older machines and is also sure it won't affect the application's behavior, then he can read the Doc and properly provided a -smp cmdline with "strict=on" to boot a VM.
- We don't need to bother guessing different formats of -smp command
lines in parsing. If the new parameter is not specified or "strict=off" is provided, we totally follow the rules in smp_parse() and disable the topology exposure. And if "strict=on" is provided, we enable the topology exposure and enforce completely detailed configuration like "-smp strict=on,cpus=4,sockets=2,cores=2".
IMO, threads should also be required here. Libvirt requires all of them if one of sockets/cores/threads is provided. So if we hope to be consistent with Libvirt, the required configuration should at least "-smp strict=on,cpus=4,sockets=2,cores=2,threads=1".
Thanks, Yanan
But maxcpus will be optional, it will default to cpus if not provided. We also ensure it matches cpus if provided, given that cpu hotplug is not available yet.
Thanks, Yanan
Thanks, drew
.
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Andrew Jones -
Salil Mehta -
wangyanan (Y)