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 | Mon, 27 Jun 2022 16:16:33 +0800 |
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On 2022/6/26 20:13, Abel Wu wrote: > > On 6/9/22 8:06 PM, 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%* >> >> 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; > > return -1; > :) >
thanks for the comment. If we've run out of nr the select_idle_cpu() will stop scanning as well, so it's unnecessary to clear the mask of cluster cpus and just return.
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