Messages in this thread | | | Date | Mon, 13 Feb 2023 22:43:28 -0800 | From | Ricardo Neri <> | Subject | Re: [PATCH v3 06/10] sched/fair: Use the prefer_sibling flag of the current sched domain |
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On Mon, Feb 13, 2023 at 01:17:09PM +0100, Dietmar Eggemann wrote: > On 10/02/2023 19:31, Ricardo Neri wrote: > > On Fri, Feb 10, 2023 at 05:12:30PM +0000, Valentin Schneider wrote: > >> On 10/02/23 17:53, Peter Zijlstra wrote: > >>> On Fri, Feb 10, 2023 at 02:54:56PM +0000, Valentin Schneider wrote: > >>> > >>>> So something like have SD_PREFER_SIBLING affect the SD it's on (and not > >>>> its parent), but remove it from the lowest non-degenerated topology level? > >>> > >>> So I was rather confused about the whole moving it between levels things > >>> this morning -- conceptually, prefer siblings says you want to try > >>> sibling domains before filling up your current domain. Now, balancing > >>> between siblings happens one level up, hence looking at child->flags > >>> makes perfect sense. > >>> > >>> But looking at the current domain and still calling it prefer sibling > >>> makes absolutely no sense what so ever. > >>> > >> > >> True :-) > >> > >>> In that confusion I think I also got the polarity wrong, I thought you > >>> wanted to kill prefer_sibling for the assymetric SMT cases, instead you > >>> want to force enable it as long as there is one SMT child around. > > > > Exactly. > > > >>> > >>> Whichever way around it we do it, I'm thinking perhaps some renaming > >>> might be in order to clarify things. > >>> > >>> How about adding a flag SD_SPREAD_TASKS, which is the effective toggle > >>> of the behaviour, but have it be set by children with SD_PREFER_SIBLING > >>> or something. > >>> > >> > >> Or entirely bin SD_PREFER_SIBLING and stick with SD_SPREAD_TASKS, but yeah > >> something along those lines. > > > > I sense a consesus towards SD_SPREAD_TASKS. > > Can you not detect the E-core dst_cpu case on MC with: > > + if (child) > + sds->prefer_sibling = child->flags & SD_PREFER_SIBLING; > + else if (sds->busiest) > + sds->prefer_sibling = sds->busiest->group_weight > 1;
Whose child wants the prefer_sibling setting? In update_sd_lb_stats(), it is set based on the flags of the destination CPU's sched domain. But when used in find_busiest_group() tasks are spread from the busiest group's child domain.
Your proposed code, also needs a check for SD_PREFER_SIBLING, no?
Thanks and BR, Ricardo
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