Messages in this thread Patch in this message | | | From | Vincent Guittot <> | Date | Fri, 22 Jan 2021 10:30:52 +0100 | Subject | Re: [PATCH v3 0/5] Scan for an idle sibling in a single pass |
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Hi Mel,
On Tue, 19 Jan 2021 at 13:02, Mel Gorman <mgorman@techsingularity.net> wrote: > > On Tue, Jan 19, 2021 at 12:33:04PM +0100, Vincent Guittot wrote: > > On Tue, 19 Jan 2021 at 12:22, Mel Gorman <mgorman@techsingularity.net> wrote: > > > > > > Changelog since v2 > > > o Remove unnecessary parameters > > > o Update nr during scan only when scanning for cpus > > > > Hi Mel, > > > > I haven't looked at your previous version mainly because I'm chasing a > > performance regression on v5.11-rcx which prevents me from testing the > > impact of your patchset on my !SMT2 system. > > Will do this as soon as this problem is fixed > > > > Thanks, that would be appreciated as I do not have access to a !SMT2 > system to do my own evaluation.
I have been able to run tests with your patchset on both large arm64 SMT4 system and small arm64 !SMT system and patch 3 is still a source of regression on both. Decreasing min number of loops to 2 instead of 4 and scaling it with smt weight doesn't seem to be a good option as regressions disappear when I remove them as I tested with the patch below
hackbench -l 2560 -g 1 on 8 cores arm64 v5.11-rc4 : 1.355 (+/- 7.96) + sis improvement : 1.923 (+/- 25%) + the patch below : 1.332 (+/- 4.95)
hackbench -l 2560 -g 256 on 8 cores arm64 v5.11-rc4 : 2.116 (+/- 4.62%) + sis improvement : 2.216 (+/- 3.84%) + the patch below : 2.113 (+/- 3.01%)
So starting with a min of 2 loops instead of 4 currently and scaling nr loop with smt weight doesn't seem to be a good option and we should remove it for now
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index 808e40d0439d..c4de33574e6e 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -6138,7 +6138,7 @@ static inline int select_idle_core(struct task_struct *p, int core, struct cpuma
#endif /* CONFIG_SCHED_SMT */
-#define sis_min_cores 2 +#define sis_min_cores 4
/* * Scan the LLC domain for idle CPUs; this is dynamically regulated by @@ -6176,8 +6176,6 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t else nr = sis_min_cores;
- nr *= sched_smt_weight; - time = cpu_clock(this); }
> > -- > Mel Gorman > SUSE Labs
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