Messages in this thread | | | Subject | Re: [PATCH v4 2/2] sched/fair: Scan cluster before scanning LLC in wake-up path | From | Yicong Yang <> | Date | Fri, 10 Jun 2022 14:39:38 +0800 |
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On 2022/6/10 6:47, Tim Chen wrote: > On Thu, 2022-06-09 at 20:06 +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: >> 5.19-rc1 patched >> Hmean 1 350.27 ( 0.00%) 406.88 * 16.16%* >> Hmean 2 702.01 ( 0.00%) 808.22 * 15.13%* >> Hmean 4 1405.14 ( 0.00%) 1614.34 * 14.89%* >> Hmean 8 2830.53 ( 0.00%) 3169.02 * 11.96%* >> Hmean 16 5597.95 ( 0.00%) 6224.20 * 11.19%* >> Hmean 32 10537.38 ( 0.00%) 10524.97 * -0.12%* >> Hmean 64 8366.04 ( 0.00%) 8437.41 * 0.85%* >> Hmean 128 7060.87 ( 0.00%) 7150.25 * 1.27%* >> >> On numa 0-1: >> 5.19-rc1 patched >> Hmean 1 346.11 ( 0.00%) 408.47 * 18.02%* >> Hmean 2 693.34 ( 0.00%) 805.78 * 16.22%* >> Hmean 4 1384.96 ( 0.00%) 1602.49 * 15.71%* >> Hmean 8 2699.45 ( 0.00%) 3069.98 * 13.73%* >> Hmean 16 5327.11 ( 0.00%) 5688.19 * 6.78%* >> Hmean 32 10019.10 ( 0.00%) 11862.56 * 18.40%* >> Hmean 64 13850.57 ( 0.00%) 17748.54 * 28.14%* >> Hmean 128 12498.25 ( 0.00%) 15541.59 * 24.35%* >> Hmean 256 11195.77 ( 0.00%) 13854.06 * 23.74%* > > Yicong, > > Have you tried any workload where tasks don't share data > with each other but have sleep/wakeup? That's the case > where we actually want to spread the tasks out among the clusters > to void contention for L2 cache. > > Will be nice to make sure there's no regression there for > such workload. >
Any certain workload you'd like me test? I'm willing to do :)
I've tested this patch with MySQL as well (like in v2). This won't hurt the MySQL case with SIS_PROP but observed some improvement with SIS_UTIL posted in [1]. We leverage the nr to suppress redundant scanning in the current approach and seems SIS_UTIL is more efficient in this case.
5.19-rc1 patched patched+SIS_UTIL[1] TPS-16threads 6215.11 6172.74 (-0.68%) 6217.33 (0.04%) QPS-16threads 124302.21 123454.68 (-0.68%) 124346.52 (0.04%) avg-lat-16threads 2.57 2.59 (-0.65%) 2.57 (0.00%) TPS-24threads 8726.40 8690.87 (-0.41%) 8833.08 (1.22%) QPS-24threads 174527.88 173817.42 (-0.41%) 176661.54 (1.21%) avg-lat-24threads 2.75 2.76 (-0.36%) 2.71 (1.33%) TPS-32threads 9555.42 9514.86 (-0.42%) 10010.87 (4.77%) QPS-32threads 191108.37 190297.28 (-0.42%) 200217.35 (4.55%) avg-lat-32threads 3.35 3.36 (-0.30%) 3.20 (4.58%) TPS-64threads 10290.10 10324.75 (0.34%) 10819.77 (5.15%) QPS-64threads 205802.05 206494.95 (0.34%) 216395.40 (4.90%) avg-lat-64threads 6.22 6.20 (0.38%) 5.92 (4.88%)
> Code itself looks good. > > Reviewed-by: Tim Chen <tim.c.chen@linux.intel.com> >
Thanks.
[1] https://lore.kernel.org/lkml/20220428182442.659294-1-yu.c.chen@intel.com/
>> >> 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 | 44 +++++++++++++++++++++++++++++++++++++++++--- >> 1 file changed, 41 insertions(+), 3 deletions(-) >> >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c >> index 77b2048a9326..6d173e196ad3 100644 >> --- a/kernel/sched/fair.c >> +++ b/kernel/sched/fair.c >> @@ -6327,6 +6327,40 @@ 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, struct cpumask *cpus, >> + int target, int *nr) >> +{ >> + struct sched_domain *sd = rcu_dereference(per_cpu(sd_cluster, target)); >> + int cpu, idle_cpu; >> + >> + /* TODO: Support SMT system with cluster topology */ >> + if (!sched_smt_active() && sd) { >> + for_each_cpu_and(cpu, cpus, sched_domain_span(sd)) { >> + if (!--*nr) >> + break; >> + >> + idle_cpu = __select_idle_cpu(cpu, p); >> + if ((unsigned int)idle_cpu < nr_cpumask_bits) >> + return idle_cpu; >> + } >> + >> + cpumask_andnot(cpus, cpus, sched_domain_span(sd)); >> + } >> + >> + return -1; >> +} >> +#else >> +static inline int scan_cluster(struct task_struct *p, struct cpumask *cpus, >> + int target, int *nr) >> +{ >> + return -1; >> +} >> +#endif >> + >> /* >> * Scan the LLC domain for idle CPUs; this is dynamically regulated by >> * comparing the average scan cost (tracked in sd->avg_scan_cost) against the >> @@ -6375,6 +6409,10 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool >> time = cpu_clock(this); >> } >> >> + idle_cpu = scan_cluster(p, cpus, target, &nr); >> + if ((unsigned int)idle_cpu < nr_cpumask_bits) >> + return idle_cpu; >> + >> for_each_cpu_wrap(cpu, cpus, target + 1) { >> if (has_idle_core) { >> i = select_idle_core(p, cpu, cpus, &idle_cpu); >> @@ -6382,7 +6420,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool >> return i; >> >> } else { >> - if (!--nr) >> + if (--nr <= 0) >> return -1; >> idle_cpu = __select_idle_cpu(cpu, p); >> if ((unsigned int)idle_cpu < nr_cpumask_bits) >> @@ -6481,7 +6519,7 @@ 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; >> @@ -6507,7 +6545,7 @@ 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)) { > > > . >
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