Messages in this thread | | | Subject | Re: [PATCH v2 2/2] sched/fair: Scan cluster before scanning LLC in wake-up path | From | Yicong Yang <> | Date | Thu, 27 Jan 2022 10:02:37 +0800 |
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On 2022/1/27 9:14, Tim Chen wrote: > On Wed, 2022-01-26 at 16:09 +0800, Yicong Yang wrote: >> From: Barry Song <song.bao.hua@hisilicon.com> >> >> For platforms having clusters like Kunpeng920, CPUs within the same >> cluster have lower latency when synchronizing and accessing shared >> resources like cache. Thus, this patch tries to find an idle cpu >> within the cluster of the target CPU before scanning the whole LLC >> to gain lower latency. >> >> Note neither Kunpeng920 nor x86 Jacobsville supports SMT, so this >> patch doesn't consider SMT for this moment. >> >> Testing has been done on Kunpeng920 by pinning tasks to one numa >> and two numa. On Kunpeng920, Each numa has 8 clusters and each >> cluster has 4 CPUs. >> >> With this patch, We noticed enhancement on tbench within one >> numa or cross two numa. >> >> On numa 0: >> 5.17-rc1 patched >> Hmean 1 324.73 ( 0.00%) 378.01 * 16.41%* >> Hmean 2 645.36 ( 0.00%) 754.63 * 16.93%* >> Hmean 4 1302.09 ( 0.00%) 1507.54 * 15.78%* >> Hmean 8 2612.03 ( 0.00%) 2982.57 * 14.19%* >> Hmean 16 5307.12 ( 0.00%) 5886.66 * 10.92%* >> Hmean 32 9354.22 ( 0.00%) 9908.13 * 5.92%* >> Hmean 64 7240.35 ( 0.00%) 7278.78 * 0.53%* >> Hmean 128 6186.40 ( 0.00%) 6187.85 ( 0.02%) >> >> On numa 0-1: >> 5.17-rc1 patched >> Hmean 1 320.01 ( 0.00%) 378.44 * 18.26%* >> Hmean 2 643.85 ( 0.00%) 752.52 * 16.88%* >> Hmean 4 1287.36 ( 0.00%) 1505.62 * 16.95%* >> Hmean 8 2564.60 ( 0.00%) 2955.29 * 15.23%* >> Hmean 16 5195.69 ( 0.00%) 5814.74 * 11.91%* >> Hmean 32 9769.16 ( 0.00%) 10872.63 * 11.30%* >> Hmean 64 15952.50 ( 0.00%) 17281.98 * 8.33%* >> Hmean 128 13113.77 ( 0.00%) 13895.20 * 5.96%* >> Hmean 256 10997.59 ( 0.00%) 11244.69 * 2.25%* >> Hmean 512 14623.60 ( 0.00%) 15526.25 * 6.17%* >> >> This will also help to improve the MySQL. With MySQL server >> running on numa 0 and client running on numa 1, both QPS and >> latency is imporved on read-write case: >> 5.17-rc1 patched >> QPS-16threads 143333.2633 145077.4033(+1.22%) >> QPS-24threads 195085.9367 202719.6133(+3.91%) >> QPS-32threads 241165.6867 249020.74(+3.26%) >> QPS-64threads 244586.8433 253387.7567(+3.60%) >> avg-lat-16threads 2.23 2.19(+1.19%) >> avg-lat-24threads 2.46 2.36(+3.79%) >> avg-lat-36threads 2.66 2.57(+3.26%) >> avg-lat-64threads 5.23 5.05(+3.44%) >> >> Tested-by: Yicong Yang <yangyicong@hisilicon.com> >> Signed-off-by: Barry Song <song.bao.hua@hisilicon.com> >> Signed-off-by: Yicong Yang <yangyicong@hisilicon.com> >> --- >> kernel/sched/fair.c | 46 +++++++++++++++++++++++++++++++++++++++++ >> ---- >> 1 file changed, 42 insertions(+), 4 deletions(-) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index 5146163bfabb..2f84a933aedd 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -6262,12 +6262,46 @@ static inline int select_idle_smt(struct >> task_struct *p, struct sched_domain *sd >> >> #endif /* CONFIG_SCHED_SMT */ >> >> +#ifdef CONFIG_SCHED_CLUSTER >> +/* >> + * Scan the cluster domain for idle CPUs and clear cluster cpumask >> after scanning >> + */ >> +static inline int scan_cluster(struct task_struct *p, int prev_cpu, >> int target) >> +{ >> + struct cpumask *cpus = >> this_cpu_cpumask_var_ptr(select_idle_mask); >> + struct sched_domain *sd = rcu_dereference(per_cpu(sd_cluster, >> target)); >> + int cpu, idle_cpu; >> + >> + /* TODO: Support SMT case while a machine with both cluster and >> SMT born */ > > This is probably a clearer comment > > /* TODO: Support SMT system with cluster topology */ > >> + if (!sched_smt_active() && sd) { >> + for_each_cpu_and(cpu, cpus, sched_domain_span(sd)) { >> + idle_cpu = __select_idle_cpu(cpu, p); >> */ >> -static int select_idle_cpu(struct task_struct *p, struct >> sched_domain *sd, bool has_idle_core, int target) >> +static int select_idle_cpu(struct task_struct *p, struct >> sched_domain *sd, bool has_idle_core, int prev_cpu, int target) >> { >> struct cpumask *cpus = >> this_cpu_cpumask_var_ptr(select_idle_mask); >> int i, cpu, idle_cpu = -1, nr = INT_MAX; >> @@ -6282,6 +6316,10 @@ static int select_idle_cpu(struct task_struct >> *p, struct sched_domain *sd, bool >> >> cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr); >> >> + idle_cpu = scan_cluster(p, prev_cpu, target); > > Shouldn't "cpus" from > > cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr); > > be passed to scan_cluster, to make sure that the cpu returned is > in the affinity mask of the task? I don't see p->cpus_ptr > being checked in scan_cluster to make sure the cpu found is in the > affinity mask. >
The cpus scanned in scan_cluster() is the intersection of select_idle_mask and sched_domain_span(cluster_sd), and we limited the select_idle_mask in the tasks' affinity mask before we enter scan_cluster() here.
Thanks.
> Tim > > >> + if ((unsigned int)idle_cpu < nr_cpumask_bits) >> + return idle_cpu; >> + >> if (sched_feat(SIS_PROP) && !has_idle_core) { >> u64 avg_cost, avg_idle, span_avg; >> unsigned long now = jiffies; >> @@ -6416,7 +6454,7 @@ static int select_idle_sibling(struct >> task_struct *p, int prev, int target) >> /* >> * If the previous CPU is cache affine and idle, don't be >> stupid: >> */ >> - if (prev != target && cpus_share_cache(prev, target) && >> + if (prev != target && cpus_share_resources(prev, target) && >> (available_idle_cpu(prev) || sched_idle_cpu(prev)) && >> asym_fits_capacity(task_util, prev)) >> return prev; >> @@ -6442,7 +6480,7 @@ static int select_idle_sibling(struct >> task_struct *p, int prev, int target) >> p->recent_used_cpu = prev; >> if (recent_used_cpu != prev && >> recent_used_cpu != target && >> - cpus_share_cache(recent_used_cpu, target) && >> + cpus_share_resources(recent_used_cpu, target) && >> (available_idle_cpu(recent_used_cpu) || >> sched_idle_cpu(recent_used_cpu)) && >> cpumask_test_cpu(p->recent_used_cpu, p->cpus_ptr) && >> asym_fits_capacity(task_util, recent_used_cpu)) { >> @@ -6483,7 +6521,7 @@ static int select_idle_sibling(struct >> task_struct *p, int prev, int target) >> } >> } >> >> - i = select_idle_cpu(p, sd, has_idle_core, target); >> + i = select_idle_cpu(p, sd, has_idle_core, prev, target); >> if ((unsigned)i < nr_cpumask_bits) >> return i; >> > > . >
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