Messages in this thread | | | Date | Tue, 23 Aug 2022 16:09:54 +0800 | From | Chen Yu <> | Subject | Re: [PATCH v7 2/2] sched/fair: Scan cluster before scanning LLC in wake-up path |
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On 2022-08-23 at 15:48:00 +0800, Yicong Yang wrote: > On 2022/8/23 11:45, Chen Yu wrote: > > On 2022-08-22 at 15:36:10 +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. > >> > >> 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: > >> 6.0-rc1 patched > >> Hmean 1 351.20 ( 0.00%) 396.45 * 12.88%* > >> Hmean 2 700.43 ( 0.00%) 793.76 * 13.32%* > >> Hmean 4 1404.42 ( 0.00%) 1583.62 * 12.76%* > >> Hmean 8 2833.31 ( 0.00%) 3147.85 * 11.10%* > >> Hmean 16 5501.90 ( 0.00%) 6089.89 * 10.69%* > >> Hmean 32 10428.59 ( 0.00%) 10619.63 * 1.83%* > >> Hmean 64 8223.39 ( 0.00%) 8306.93 * 1.02%* > >> Hmean 128 7042.88 ( 0.00%) 7068.03 * 0.36%* > >> > >> On numa 0-1: > >> 6.0-rc1 patched > >> Hmean 1 363.06 ( 0.00%) 397.13 * 9.38%* > >> Hmean 2 721.68 ( 0.00%) 789.84 * 9.44%* > >> Hmean 4 1435.15 ( 0.00%) 1566.01 * 9.12%* > >> Hmean 8 2776.17 ( 0.00%) 3007.05 * 8.32%* > >> Hmean 16 5471.71 ( 0.00%) 6103.91 * 11.55%* > >> Hmean 32 10164.98 ( 0.00%) 11531.81 * 13.45%* > >> Hmean 64 17143.28 ( 0.00%) 20078.68 * 17.12%* > >> Hmean 128 14552.70 ( 0.00%) 15156.41 * 4.15%* > >> Hmean 256 12827.37 ( 0.00%) 13326.86 * 3.89%* > >> > >> Note neither Kunpeng920 nor x86 Jacobsville supports SMT, so the SMT branch > >> in the code has not been tested but it supposed to work. > >> > >> Suggested-by: Peter Zijlstra <peterz@infradead.org> > >> [https://lore.kernel.org/lkml/Ytfjs+m1kUs0ScSn@worktop.programming.kicks-ass.net] > >> 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> > >> Reviewed-by: Tim Chen <tim.c.chen@linux.intel.com> > >> --- > >> kernel/sched/fair.c | 30 +++++++++++++++++++++++++++--- > >> kernel/sched/sched.h | 2 ++ > >> kernel/sched/topology.c | 10 ++++++++++ > >> 3 files changed, 39 insertions(+), 3 deletions(-) > >> > >> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > >> index 914096c5b1ae..6fa77610d0f5 100644 > >> --- a/kernel/sched/fair.c > >> +++ b/kernel/sched/fair.c > >> @@ -6437,6 +6437,30 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, bool > >> } > >> } > >> > >> + if (static_branch_unlikely(&sched_cluster_active)) { > >> + struct sched_domain *sdc = rcu_dereference(per_cpu(sd_cluster, target)); > >> + > >> + if (sdc) { > >> + for_each_cpu_wrap(cpu, sched_domain_span(sdc), target + 1) { > > Looks good to me. One minor question, why don't we use > > cpumask_and(cpus, sched_domain_span(sdc), cpus); > >> + if (!cpumask_test_cpu(cpu, cpus)) > >> + continue; > > so above check can be removed in each loop? > > Since we'll need to recalculate the mask of rest CPUs to test in the LLC after scanning the cluster CPUs. > I was thinking of introducing a temporary variable cpumask_and(cpus_cluster, sched_domain_span(sdc), cpus); and iterate this cpus_cluster in the loop. But since the cpus is reused, it is ok to be as it is. > > Besides may I know what version this patch > > is based on? since I failed to apply the patch on v6.0-rc2. Other than that: > > > > It's on 6.0-rc1 when sent but can be cleanly rebased on rc2: > > yangyicong@ubuntu:~/mainline_linux/linux_sub_workspace$ git log --oneline -3 > 0079c27ba265 (HEAD -> topost-cls-v7, topost-cls-v6) sched/fair: Scan cluster before scanning LLC in wake-up path > 1ecb9e322bd7 sched: Add per_cpu cluster domain info and cpus_share_lowest_cache API I did not apply 1/2, and that was why it failed I think. Thanks for explaination.
Thanks, Chenyu > 1c23f9e627a7 (tag: v6.0-rc2, origin/master, origin/HEAD, master) Linux 6.0-rc2 > > So I'm not sure where's the problem... > > > Reviewed-by: Chen Yu <yu.c.chen@intel.com> > > > > Thanks! > > > thanks, > > Chenyu > >> + > >> + if (has_idle_core) { > >> + i = select_idle_core(p, cpu, cpus, &idle_cpu); > >> + if ((unsigned int)i < nr_cpumask_bits) > >> + return i; > >> + } else { > >> + if (--nr <= 0) > >> + return -1; > >> + 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(sdc)); > >> + } > >> + } > > . > >
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