From: James Morse james.morse@arm.com
maillist inclusion category: feature bugzilla: https://gitee.com/openeuler/kernel/issues/I8T2RT
Reference: https://git.kernel.org/pub/scm/linux/kernel/git/morse/linux.git/log/?h=mpam/...
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Intel is blessed with an abundance of monitors, one per RMID, that can be read from any CPU in the domain. MPAMs monitors reside in the MMIO MSC, the number implemented is up to the manufacturer. This means when there are fewer monitors than needed, they need to be allocated and freed.
MPAM's CSU monitors are used to back the 'llc_occupancy' monitor file. The CSU counter is allowed to return 'not ready' for a small number of micro-seconds after programming. To allow one CSU hardware monitor to be used for multiple control or monitor groups, the CPU accessing the monitor needs to be able to block when configuring and reading the counter.
Worse, the domain may be broken up into slices, and the MMIO accesses for each slice may need performing from different CPUs.
These two details mean MPAMs monitor code needs to be able to sleep, and IPI another CPU in the domain to read from a resource that has been sliced.
mon_event_read() already invokes mon_event_count() via IPI, which means this isn't possible. On systems using nohz-full, some CPUs need to be interrupted to run kernel work as they otherwise stay in user-space running realtime workloads. Interrupting these CPUs should be avoided, and scheduling work on them may never complete.
Change mon_event_read() to pick a housekeeping CPU, (one that is not using nohz_full) and schedule mon_event_count() and wait. If all the CPUs in a domain are using nohz-full, then an IPI is used as the fallback.
This function is only used in response to a user-space filesystem request (not the timing sensitive overflow code).
This allows MPAM to hide the slice behaviour from resctrl, and to keep the monitor-allocation in monitor.c. When the IPI fallback is used on machines where MPAM needs to make an access on multiple CPUs, the counter read will always fail.
Signed-off-by: James Morse james.morse@arm.com Tested-by: Shaopeng Tan tan.shaopeng@fujitsu.com Tested-by: Peter Newman peternewman@google.com Tested-by: Babu Moger babu.moger@amd.com Reviewed-by: Shaopeng Tan tan.shaopeng@fujitsu.com Reviewed-by: Peter Newman peternewman@google.com Reviewed-by: Reinette Chatre reinette.chatre@intel.com Signed-off-by: Zeng Heng zengheng4@huawei.com --- arch/x86/kernel/cpu/resctrl/ctrlmondata.c | 26 +++++++++++++++++++++-- arch/x86/kernel/cpu/resctrl/monitor.c | 2 +- 2 files changed, 25 insertions(+), 3 deletions(-)
diff --git a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c index beccb0e87ba7..d07f99245851 100644 --- a/arch/x86/kernel/cpu/resctrl/ctrlmondata.c +++ b/arch/x86/kernel/cpu/resctrl/ctrlmondata.c @@ -19,6 +19,8 @@ #include <linux/kernfs.h> #include <linux/seq_file.h> #include <linux/slab.h> +#include <linux/tick.h> + #include "internal.h"
/* @@ -522,12 +524,21 @@ int rdtgroup_schemata_show(struct kernfs_open_file *of, return ret; }
+static int smp_mon_event_count(void *arg) +{ + mon_event_count(arg); + + return 0; +} + void mon_event_read(struct rmid_read *rr, struct rdt_resource *r, struct rdt_domain *d, struct rdtgroup *rdtgrp, int evtid, int first) { + int cpu; + /* - * setup the parameters to send to the IPI to read the data. + * Setup the parameters to pass to mon_event_count() to read the data. */ rr->rgrp = rdtgrp; rr->evtid = evtid; @@ -536,7 +547,18 @@ void mon_event_read(struct rmid_read *rr, struct rdt_resource *r, rr->val = 0; rr->first = first;
- smp_call_function_any(&d->cpu_mask, mon_event_count, rr, 1); + cpu = cpumask_any_housekeeping(&d->cpu_mask); + + /* + * cpumask_any_housekeeping() prefers housekeeping CPUs, but + * are all the CPUs nohz_full? If yes, pick a CPU to IPI. + * MPAM's resctrl_arch_rmid_read() is unable to read the + * counters on some platforms if its called in irq context. + */ + if (tick_nohz_full_cpu(cpu)) + smp_call_function_any(&d->cpu_mask, mon_event_count, rr, 1); + else + smp_call_on_cpu(cpu, smp_mon_event_count, rr, false); }
int rdtgroup_mondata_show(struct seq_file *m, void *arg) diff --git a/arch/x86/kernel/cpu/resctrl/monitor.c b/arch/x86/kernel/cpu/resctrl/monitor.c index 8737a9d6caef..7e81268137b0 100644 --- a/arch/x86/kernel/cpu/resctrl/monitor.c +++ b/arch/x86/kernel/cpu/resctrl/monitor.c @@ -588,7 +588,7 @@ static void mbm_bw_count(u32 closid, u32 rmid, struct rmid_read *rr) }
/* - * This is called via IPI to read the CQM/MBM counters + * This is scheduled by mon_event_read() to read the CQM/MBM counters * on a domain. */ void mon_event_count(void *info)