As long as NUMA diameter > 2, building sched_domain by sibling's child domain will definitely create a sched_domain with sched_group which will span out of the sched_domain +------+ +------+ +-------+ +------+ | node | 12 |node | 20 | node | 12 |node | | 0 +---------+1 +--------+ 2 +-------+3 | +------+ +------+ +-------+ +------+

domain0 node0 node1 node2 node3

domain1 node0+1 node0+1 node2+3 node2+3 + domain2 node0+1+2 | group: node0+1 | group:node2+3 <-------------------+

when node2 is added into the domain2 of node0, kernel is using the child domain of node2's domain2, which is domain1(node2+3). Node 3 is outside the span of the domain including node0+1+2.

This will make load_balance() and select_task_rq_fair() run on wrong CPU and base on avg load.

here we move to use the *child* domain of the *child* domain of node2's domain2 to build the sched_group.

+------+ +------+ +-------+ +------+ | node | 12 |node | 20 | node | 12 |node | | 0 +---------+1 +--------+ 2 +-------+3 | +------+ +------+ +-------+ +------+

domain0 node0 node1 +- node2 node3 | domain1 node0+1 node0+1 | node2+3 node2+3 | domain2 node0+1+2 | group: node0+1 | group:node2 <-------------------+

A tricky thing is that we shouldn't use the first cpu of node2 as the unique ID for the sched_group generated by grandchild, otherwise, when this cpu becomes the balance_cpu of another sched_group of cpus other than node0, our sched_group generated by grandchild will have same ID with another sched_group generated by child in init_overlap_sched_group(): build_balance_mask(sd, sg, mask); cpu = cpumask_first_and(sched_group_span(sg), mask);

sg->sgc = *per_cpu_ptr(sdd->sgc, cpu); So here we move to use the second cpu. But we can put the cpu back during load_balance by using sched_group_span rather than group_balance_mask. For the corner case, if NUMA has only one CPU, we will get to a warning WARN_ON_ONCE here: static void init_overlap_sched_group(struct sched_domain *sd, struct sched_group *sg) { if (atomic_inc_return(&sg->sgc->ref) == 1) cpumask_copy(group_balance_mask(sg), mask); else WARN_ON_ONCE(!cpumask_equal(group_balance_mask(sg), mask)); } But It is pretty much not a real case.

Tested by the below topology: qemu-system-aarch64 -M virt -nographic \ -smp cpus=8 \ -numa node,cpus=0-1,nodeid=0 \ -numa node,cpus=2-3,nodeid=1 \ -numa node,cpus=4-5,nodeid=2 \ -numa node,cpus=6-7,nodeid=3 \ -numa dist,src=0,dst=1,val=12 \ -numa dist,src=0,dst=2,val=20 \ -numa dist,src=0,dst=3,val=22 \ -numa dist,src=1,dst=2,val=22 \ -numa dist,src=2,dst=3,val=12 \ -numa dist,src=1,dst=3,val=24 \ -m 4G -cpu cortex-a57 -kernel arch/arm64/boot/Image

w/o patch, we get lots of "groups don't span domain->span": [ 0.802139] CPU0 attaching sched-domain(s): [ 0.802193] domain-0: span=0-1 level=MC [ 0.802443] groups: 0:{ span=0 cap=1013 }, 1:{ span=1 cap=979 } [ 0.802693] domain-1: span=0-3 level=NUMA [ 0.802731] groups: 0:{ span=0-1 cap=1992 }, 2:{ span=2-3 cap=1943 } [ 0.802811] domain-2: span=0-5 level=NUMA [ 0.802829] groups: 0:{ span=0-3 cap=3935 }, 4:{ span=4-7 cap=3937 } [ 0.802881] ERROR: groups don't span domain->span [ 0.803058] domain-3: span=0-7 level=NUMA [ 0.803080] groups: 0:{ span=0-5 mask=0-1 cap=5843 }, 6:{ span=4-7 mask=6-7 cap=4077 } [ 0.804055] CPU1 attaching sched-domain(s): [ 0.804072] domain-0: span=0-1 level=MC [ 0.804096] groups: 1:{ span=1 cap=979 }, 0:{ span=0 cap=1013 } [ 0.804152] domain-1: span=0-3 level=NUMA [ 0.804170] groups: 0:{ span=0-1 cap=1992 }, 2:{ span=2-3 cap=1943 } [ 0.804219] domain-2: span=0-5 level=NUMA [ 0.804236] groups: 0:{ span=0-3 cap=3935 }, 4:{ span=4-7 cap=3937 } [ 0.804302] ERROR: groups don't span domain->span [ 0.804520] domain-3: span=0-7 level=NUMA [ 0.804546] groups: 0:{ span=0-5 mask=0-1 cap=5843 }, 6:{ span=4-7 mask=6-7 cap=4077 } [ 0.804677] CPU2 attaching sched-domain(s): [ 0.804687] domain-0: span=2-3 level=MC [ 0.804705] groups: 2:{ span=2 cap=934 }, 3:{ span=3 cap=1009 } [ 0.804754] domain-1: span=0-3 level=NUMA [ 0.804772] groups: 2:{ span=2-3 cap=1943 }, 0:{ span=0-1 cap=1992 } [ 0.804820] domain-2: span=0-5 level=NUMA [ 0.804836] groups: 2:{ span=0-3 mask=2-3 cap=3991 }, 4:{ span=0-1,4-7 mask=4-5 cap=5985 } [ 0.804944] ERROR: groups don't span domain->span [ 0.805108] domain-3: span=0-7 level=NUMA [ 0.805134] groups: 2:{ span=0-5 mask=2-3 cap=5899 }, 6:{ span=0-1,4-7 mask=6-7 cap=6125 } [ 0.805223] CPU3 attaching sched-domain(s): [ 0.805232] domain-0: span=2-3 level=MC [ 0.805249] groups: 3:{ span=3 cap=1009 }, 2:{ span=2 cap=934 } [ 0.805319] domain-1: span=0-3 level=NUMA [ 0.805336] groups: 2:{ span=2-3 cap=1943 }, 0:{ span=0-1 cap=1992 } [ 0.805383] domain-2: span=0-5 level=NUMA [ 0.805399] groups: 2:{ span=0-3 mask=2-3 cap=3991 }, 4:{ span=0-1,4-7 mask=4-5 cap=5985 } [ 0.805458] ERROR: groups don't span domain->span [ 0.805605] domain-3: span=0-7 level=NUMA [ 0.805626] groups: 2:{ span=0-5 mask=2-3 cap=5899 }, 6:{ span=0-1,4-7 mask=6-7 cap=6125 } [ 0.805712] CPU4 attaching sched-domain(s): [ 0.805721] domain-0: span=4-5 level=MC [ 0.805738] groups: 4:{ span=4 cap=984 }, 5:{ span=5 cap=924 } [ 0.805787] domain-1: span=4-7 level=NUMA [ 0.805803] groups: 4:{ span=4-5 cap=1908 }, 6:{ span=6-7 cap=2029 } [ 0.805851] domain-2: span=0-1,4-7 level=NUMA [ 0.805867] groups: 4:{ span=4-7 cap=3937 }, 0:{ span=0-3 cap=3935 } [ 0.805915] ERROR: groups don't span domain->span [ 0.806108] domain-3: span=0-7 level=NUMA [ 0.806130] groups: 4:{ span=0-1,4-7 mask=4-5 cap=5985 }, 2:{ span=0-3 mask=2-3 cap=3991 } [ 0.806214] CPU5 attaching sched-domain(s): [ 0.806222] domain-0: span=4-5 level=MC [ 0.806240] groups: 5:{ span=5 cap=924 }, 4:{ span=4 cap=984 } [ 0.806841] domain-1: span=4-7 level=NUMA [ 0.806866] groups: 4:{ span=4-5 cap=1908 }, 6:{ span=6-7 cap=2029 } [ 0.806934] domain-2: span=0-1,4-7 level=NUMA [ 0.806953] groups: 4:{ span=4-7 cap=3937 }, 0:{ span=0-3 cap=3935 } [ 0.807004] ERROR: groups don't span domain->span [ 0.807312] domain-3: span=0-7 level=NUMA [ 0.807386] groups: 4:{ span=0-1,4-7 mask=4-5 cap=5985 }, 2:{ span=0-3 mask=2-3 cap=3991 } [ 0.807686] CPU6 attaching sched-domain(s): [ 0.807710] domain-0: span=6-7 level=MC [ 0.807750] groups: 6:{ span=6 cap=1017 }, 7:{ span=7 cap=1012 } [ 0.807840] domain-1: span=4-7 level=NUMA [ 0.807870] groups: 6:{ span=6-7 cap=2029 }, 4:{ span=4-5 cap=1908 } [ 0.807952] domain-2: span=0-1,4-7 level=NUMA [ 0.807985] groups: 6:{ span=4-7 mask=6-7 cap=4077 }, 0:{ span=0-5 mask=0-1 cap=5843 } [ 0.808045] ERROR: groups don't span domain->span [ 0.808257] domain-3: span=0-7 level=NUMA [ 0.808571] groups: 6:{ span=0-1,4-7 mask=6-7 cap=6125 }, 2:{ span=0-5 mask=2-3 cap=5899 } [ 0.808848] CPU7 attaching sched-domain(s): [ 0.808860] domain-0: span=6-7 level=MC [ 0.808880] groups: 7:{ span=7 cap=1012 }, 6:{ span=6 cap=1017 } [ 0.808953] domain-1: span=4-7 level=NUMA [ 0.808974] groups: 6:{ span=6-7 cap=2029 }, 4:{ span=4-5 cap=1908 } [ 0.809034] domain-2: span=0-1,4-7 level=NUMA [ 0.809055] groups: 6:{ span=4-7 mask=6-7 cap=4077 }, 0:{ span=0-5 mask=0-1 cap=5843 } [ 0.809128] ERROR: groups don't span domain->span [ 0.810361] domain-3: span=0-7 level=NUMA [ 0.810400] groups: 6:{ span=0-1,4-7 mask=6-7 cap=5961 }, 2:{ span=0-5 mask=2-3 cap=5903 }

w/ patch, we get no "groups don't span domain->span": [ 0.868907] CPU0 attaching sched-domain(s): [ 0.868962] domain-0: span=0-1 level=MC [ 0.869179] groups: 0:{ span=0 cap=1013 }, 1:{ span=1 cap=983 } [ 0.869405] domain-1: span=0-3 level=NUMA [ 0.869438] groups: 0:{ span=0-1 cap=1996 }, 2:{ span=2-3 cap=2006 } [ 0.869542] domain-2: span=0-5 level=NUMA [ 0.869559] groups: 0:{ span=0-3 cap=4002 }, 5:{ span=4-5 cap=2048 } [ 0.869603] domain-3: span=0-7 level=NUMA [ 0.869618] groups: 0:{ span=0-5 mask=0-1 cap=5980 }, 6:{ span=4-7 mask=6-7 cap=4016 } [ 0.870303] CPU1 attaching sched-domain(s): [ 0.870314] domain-0: span=0-1 level=MC [ 0.870334] groups: 1:{ span=1 cap=983 }, 0:{ span=0 cap=1013 } [ 0.870381] domain-1: span=0-3 level=NUMA [ 0.870396] groups: 0:{ span=0-1 cap=1996 }, 2:{ span=2-3 cap=2006 } [ 0.870440] domain-2: span=0-5 level=NUMA [ 0.870454] groups: 0:{ span=0-3 cap=4002 }, 5:{ span=4-5 cap=2048 } [ 0.870507] domain-3: span=0-7 level=NUMA [ 0.870530] groups: 0:{ span=0-5 mask=0-1 cap=5980 }, 6:{ span=4-7 mask=6-7 cap=4016 } [ 0.870611] CPU2 attaching sched-domain(s): [ 0.870619] domain-0: span=2-3 level=MC [ 0.870634] groups: 2:{ span=2 cap=1007 }, 3:{ span=3 cap=999 } [ 0.870677] domain-1: span=0-3 level=NUMA [ 0.870691] groups: 2:{ span=2-3 cap=2006 }, 0:{ span=0-1 cap=1996 } [ 0.870734] domain-2: span=0-5 level=NUMA [ 0.870748] groups: 2:{ span=0-3 mask=2-3 cap=4054 }, 5:{ span=4-5 cap=2048 } [ 0.870795] domain-3: span=0-7 level=NUMA [ 0.870809] groups: 2:{ span=0-5 mask=2-3 cap=6032 }, 6:{ span=0-1,4-7 mask=6-7 cap=6064 } [ 0.870913] CPU3 attaching sched-domain(s): [ 0.870921] domain-0: span=2-3 level=MC [ 0.870936] groups: 3:{ span=3 cap=999 }, 2:{ span=2 cap=1007 } [ 0.870979] domain-1: span=0-3 level=NUMA [ 0.870993] groups: 2:{ span=2-3 cap=2006 }, 0:{ span=0-1 cap=1996 } [ 0.871035] domain-2: span=0-5 level=NUMA [ 0.871049] groups: 2:{ span=0-3 mask=2-3 cap=4054 }, 5:{ span=4-5 cap=2048 } [ 0.871096] domain-3: span=0-7 level=NUMA [ 0.871110] groups: 2:{ span=0-5 mask=2-3 cap=6032 }, 6:{ span=0-1,4-7 mask=6-7 cap=6064 } [ 0.871177] CPU4 attaching sched-domain(s): [ 0.871185] domain-0: span=4-5 level=MC [ 0.871200] groups: 4:{ span=4 cap=977 }, 5:{ span=5 cap=1001 } [ 0.871243] domain-1: span=4-7 level=NUMA [ 0.871257] groups: 4:{ span=4-5 cap=1978 }, 6:{ span=6-7 cap=1968 } [ 0.871300] domain-2: span=0-1,4-7 level=NUMA [ 0.871314] groups: 4:{ span=4-7 cap=3946 }, 1:{ span=0-1 cap=2048 } [ 0.871356] domain-3: span=0-7 level=NUMA [ 0.871370] groups: 4:{ span=0-1,4-7 mask=4-5 cap=5994 }, 2:{ span=0-3 mask=2-3 cap=4054 } [ 0.871436] CPU5 attaching sched-domain(s): [ 0.871443] domain-0: span=4-5 level=MC [ 0.871457] groups: 5:{ span=5 cap=1001 }, 4:{ span=4 cap=977 } [ 0.871512] domain-1: span=4-7 level=NUMA [ 0.871893] groups: 4:{ span=4-5 cap=1978 }, 6:{ span=6-7 cap=1968 } [ 0.871949] domain-2: span=0-1,4-7 level=NUMA [ 0.871966] groups: 4:{ span=4-7 cap=3946 }, 1:{ span=0-1 cap=2048 } [ 0.872010] domain-3: span=0-7 level=NUMA [ 0.872025] groups: 4:{ span=0-1,4-7 mask=4-5 cap=5994 }, 2:{ span=0-3 mask=2-3 cap=4054 } [ 0.872115] CPU6 attaching sched-domain(s): [ 0.872123] domain-0: span=6-7 level=MC [ 0.872139] groups: 6:{ span=6 cap=993 }, 7:{ span=7 cap=975 } [ 0.872186] domain-1: span=4-7 level=NUMA [ 0.872202] groups: 6:{ span=6-7 cap=1968 }, 4:{ span=4-5 cap=1978 } [ 0.872246] domain-2: span=0-1,4-7 level=NUMA [ 0.872260] groups: 6:{ span=4-7 mask=6-7 cap=4016 }, 1:{ span=0-1 cap=2048 } [ 0.872309] domain-3: span=0-7 level=NUMA [ 0.872323] groups: 6:{ span=0-1,4-7 mask=6-7 cap=6064 }, 2:{ span=0-5 mask=2-3 cap=6032 } [ 0.872392] CPU7 attaching sched-domain(s): [ 0.872399] domain-0: span=6-7 level=MC [ 0.872414] groups: 7:{ span=7 cap=975 }, 6:{ span=6 cap=993 } [ 0.872458] domain-1: span=4-7 level=NUMA [ 0.872472] groups: 6:{ span=6-7 cap=1968 }, 4:{ span=4-5 cap=1978 } [ 0.872662] domain-2: span=0-1,4-7 level=NUMA [ 0.872685] groups: 6:{ span=4-7 mask=6-7 cap=4016 }, 1:{ span=0-1 cap=2048 } [ 0.872737] domain-3: span=0-7 level=NUMA [ 0.872752] groups: 6:{ span=0-1,4-7 mask=6-7 cap=6064 }, 2:{ span=0-5 mask=2-3 cap=6032 }

Reported-by: Valentin Schneider valentin.schneider@arm.com Cc: Meelis Roos mroos@linux.ee Signed-off-by: Barry Song song.bao.hua@hisilicon.com --- -v2: fix the span of sched_group rather than hacking the load balance to compensate the topology problem(thanks for the comments of Vincent and Valentin) v1 link: https://lore.kernel.org/lkml/20210115203632.34396-1-song.bao.hua@hisilicon.c...

kernel/sched/fair.c | 9 ++++- kernel/sched/sched.h | 1 + kernel/sched/topology.c | 84 ++++++++++++++++++++++++++--------------- 3 files changed, 63 insertions(+), 31 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index f183dba4961e..3ce815045793 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -9538,6 +9538,7 @@ static int should_we_balance(struct lb_env *env) { struct sched_group *sg = env->sd->groups; int cpu; + struct cpumask *mask;

/* * Ensure the balancing environment is consistent; can happen @@ -9553,8 +9554,14 @@ static int should_we_balance(struct lb_env *env) if (env->idle == CPU_NEWLY_IDLE) return 1;

+ /* + * in build_balance_mask(), we removed the first cpu from the + * balance_mask of the sched_group generated by grandchild; + * the first cpu should be able to pull task if it is idle. + */ + mask = sg->from_grandchild ? sched_group_span(sg) : group_balance_mask(sg); /* Try to find first idle CPU */ - for_each_cpu_and(cpu, group_balance_mask(sg), env->cpus) { + for_each_cpu_and(cpu, mask, env->cpus) { if (!idle_cpu(cpu)) continue;

diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index 12ada79d40f3..3ad282fdc5b1 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -1508,6 +1508,7 @@ struct sched_group { unsigned int group_weight; struct sched_group_capacity *sgc; int asym_prefer_cpu; /* CPU of highest priority in group */ + int from_grandchild; /* this sched_group comes from grandchild */

/* * The CPUs this group covers. diff --git a/kernel/sched/topology.c b/kernel/sched/topology.c index 5d3675c7a76b..23099f6dc034 100644 --- a/kernel/sched/topology.c +++ b/kernel/sched/topology.c @@ -93,7 +93,7 @@ static int sched_domain_debug_one(struct sched_domain *sd, int cpu, int level, group->sgc->id, cpumask_pr_args(sched_group_span(group)));

- if ((sd->flags & SD_OVERLAP) && + if ((sd->flags & SD_OVERLAP) && !group->from_grandchild && !cpumask_equal(group_balance_mask(group), sched_group_span(group))) { printk(KERN_CONT " mask=%*pbl", cpumask_pr_args(group_balance_mask(group))); @@ -723,35 +723,6 @@ cpu_attach_domain(struct sched_domain *sd, struct root_domain *rd, int cpu) for (tmp = sd; tmp; tmp = tmp->parent) numa_distance += !!(tmp->flags & SD_NUMA);

- /* - * FIXME: Diameter >=3 is misrepresented. - * - * Smallest diameter=3 topology is: - * - * node 0 1 2 3 - * 0: 10 20 30 40 - * 1: 20 10 20 30 - * 2: 30 20 10 20 - * 3: 40 30 20 10 - * - * 0 --- 1 --- 2 --- 3 - * - * NUMA-3 0-3 N/A N/A 0-3 - * groups: {0-2},{1-3} {1-3},{0-2} - * - * NUMA-2 0-2 0-3 0-3 1-3 - * groups: {0-1},{1-3} {0-2},{2-3} {1-3},{0-1} {2-3},{0-2} - * - * NUMA-1 0-1 0-2 1-3 2-3 - * groups: {0},{1} {1},{2},{0} {2},{3},{1} {3},{2} - * - * NUMA-0 0 1 2 3 - * - * The NUMA-2 groups for nodes 0 and 3 are obviously buggered, as the - * group span isn't a subset of the domain span. - */ - WARN_ONCE(numa_distance > 2, "Shortest NUMA path spans too many nodes\n"); - sched_domain_debug(sd, cpu);

rq_attach_root(rq, rd); @@ -906,6 +877,7 @@ build_balance_mask(struct sched_domain *sd, struct sched_group *sg, struct cpuma cpumask_clear(mask);

for_each_cpu(i, sg_span) { + int from_grandchild = 0; sibling = *per_cpu_ptr(sdd->sd, i);

/* @@ -916,10 +888,27 @@ build_balance_mask(struct sched_domain *sd, struct sched_group *sg, struct cpuma if (!sibling->child) continue;

+ while (sibling->child && + !cpumask_subset(sched_domain_span(sibling->child), + sched_domain_span(sd))) { + sibling = sibling->child; + from_grandchild = 1; + } + /* If we would not end up here, we can't continue from here */ if (!cpumask_equal(sg_span, sched_domain_span(sibling->child))) continue;

+ sg->from_grandchild = from_grandchild; + /* + * use cpu other than the first one as the unique ID of this group + * otherwise, the ID will conflict with another sched_group coming + * from child rather than grandchild + */ + if (from_grandchild && i == cpumask_first(sg_span) && + cpumask_weight(sg_span) > 1) + continue; + cpumask_set_cpu(i, mask); }

@@ -1015,6 +1004,41 @@ build_overlap_sched_groups(struct sched_domain *sd, int cpu) if (!cpumask_test_cpu(i, sched_domain_span(sibling))) continue;

+ /* + * for NUMA diameter >= 3, building sched_domain by sibling's + * child's child domain to prevent sched_group from spanning + * out of sched_domain + * if we don't do this, Diameter >=3 is misrepresented: + * + * Smallest diameter=3 topology is: + * + * node 0 1 2 3 + * 0: 10 20 30 40 + * 1: 20 10 20 30 + * 2: 30 20 10 20 + * 3: 40 30 20 10 + * + * 0 --- 1 --- 2 --- 3 + * + * NUMA-3 0-3 N/A N/A 0-3 + * groups: {0-2},{1-3} {1-3},{0-2} + * + * NUMA-2 0-2 0-3 0-3 1-3 + * groups: {0-1},{1-3} {0-2},{2-3} {1-3},{0-1} {2-3},{0-2} + * + * NUMA-1 0-1 0-2 1-3 2-3 + * groups: {0},{1} {1},{2},{0} {2},{3},{1} {3},{2} + * + * NUMA-0 0 1 2 3 + * + * The NUMA-2 groups for nodes 0 and 3 are obviously buggered, as the + * group span isn't a subset of the domain span. + */ + while (sibling->child && + !cpumask_subset(sched_domain_span(sibling->child), + span)) + sibling = sibling->child; + sg = build_group_from_child_sched_domain(sibling, cpu); if (!sg) goto fail;