From: Aubrey Li <firstname.lastname@example.org> To: Mel Gorman <email@example.com>, "Song Bao Hua (Barry Song)" <firstname.lastname@example.org> Cc: LKML <email@example.com>, Ingo Molnar <firstname.lastname@example.org>, Peter Zijlstra <email@example.com>, Vincent Guittot <firstname.lastname@example.org>, Valentin Schneider <email@example.com>, yangyicong <firstname.lastname@example.org> Subject: Re: [PATCH 8/9] sched/fair: select idle cpu from idle cpumask for task wakeup Date: Thu, 5 Aug 2021 08:23:15 +0800 [thread overview] Message-ID: <email@example.com> (raw) In-Reply-To: <20210804102613.GC6464@techsingularity.net> On 8/4/21 6:26 PM, Mel Gorman wrote: > On Mon, Aug 02, 2021 at 10:41:13AM +0000, Song Bao Hua (Barry Song) wrote: >> Hi Mel, Aubrey, >> A similar thing Yicong and me has discussed is having a mask or a count for >> idle cores. And then we can only scan idle cores in this mask in >> select_idle_cpu(). >> > > Either approach would require a lot of updates. > >> A obvious problem is that has_idle_cores is a bool, it can seriously lag >> from the real status. I mean, after system enters the status without idle >> cores, has_idle_cores could be still true. >> > > True. > >> Right now, we are setting has_idle_cores to true while cpu enters idle >> and its smt sibling is also idle. But we are setting has_idle_cores to >> false only after we scan all cores in a llc. >> >> So we have thought for a while to provide an idle core mask. But never >> really made a workable patch. >> >> Mel's patch7/9 limits the number of cores which will be scanned in >> select_idle_cpu(), it might somehow alleviate the problem we redundantly >> scan all cores while we actually have no idle core even has_idle_cores >> is true. >> > > I prototyped a patch that tracked the location of a known idle core and > use it as a starting hint for a search. It's cleared if the core is > selected for use. Unfortunately, it was not a universal win so was > dropped for the moment but either way, improving the accurate of > has_idle_cores without being too expensive would be niuce. The idle core information is already in idle cpu mask, do we have a quick and cheap way to extract out? > >> However, if we can get idle core mask, it could be also good to >> select_idle_core()? Maybe after that, we don't have to enforce >> proportional scan limits while scanning for an idle core? >> > > To remove the limits entirely, it would have to be very accurate and > it's hard to see how that can be done without having a heavily updated > shared cache line. > Bad idea, is it helpful to make a sparse cpu mask for this? :p Thanks, -Aubrey
next prev parent reply other threads:[~2021-08-04 15:16 UTC|newest] Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-07-26 10:22 [RFC PATCH 0/9] Modify and/or delete SIS_PROP Mel Gorman 2021-07-26 10:22 ` [PATCH 1/9] sched/fair: Track efficiency of select_idle_sibling Mel Gorman 2021-07-26 10:22 ` [PATCH 2/9] sched/fair: Track efficiency of task recent_used_cpu Mel Gorman 2021-07-26 10:22 ` [PATCH 3/9] sched/fair: Track efficiency of select_idle_core Mel Gorman 2021-07-26 10:22 ` [PATCH 4/9] sched/fair: Use prev instead of new target as recent_used_cpu Mel Gorman 2021-07-26 10:22 ` [PATCH 5/9] sched/fair: Avoid a second scan of target in select_idle_cpu Mel Gorman 2021-07-26 10:22 ` [PATCH 6/9] sched/fair: Make select_idle_cpu() proportional to cores Mel Gorman 2021-07-26 10:22 ` [PATCH 7/9] sched/fair: Enforce proportional scan limits when scanning for an idle core Mel Gorman 2021-08-02 10:52 ` Song Bao Hua (Barry Song) 2021-08-04 10:22 ` Mel Gorman 2021-07-26 10:22 ` [PATCH 8/9] sched/fair: select idle cpu from idle cpumask for task wakeup Mel Gorman 2021-08-02 10:41 ` Song Bao Hua (Barry Song) 2021-08-04 10:26 ` Mel Gorman 2021-08-05 0:23 ` Aubrey Li [this message] 2021-09-17 3:44 ` Barry Song 2021-09-17 4:15 ` Barry Song 2021-09-17 9:11 ` Aubrey Li 2021-09-17 13:35 ` Mel Gorman 2021-07-26 10:22 ` [PATCH 9/9] sched/core: Delete SIS_PROP and rely on the idle cpu mask Mel Gorman
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