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[73.158.249.138]) by smtp.gmail.com with ESMTPSA id fe21-20020a056a002f1500b0064d681c753csm5836265pfb.40.2023.07.13.13.12.05 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 13 Jul 2023 13:12:06 -0700 (PDT) From: Benjamin Segall To: Phil Auld Cc: linux-kernel@vger.kernel.org, Juri Lelli , Ingo Molnar , Daniel Bristot de Oliveira , Peter Zijlstra , Vincent Guittot , Dietmar Eggemann , Valentin Schneider , Steven Rostedt , Mel Gorman , Frederic Weisbecker , Tejun Heo Subject: Re: [PATCH v2 1/2] sched, cgroup: Restore meaning to hierarchical_quota References: <20230712133357.381137-1-pauld@redhat.com> <20230712133357.381137-2-pauld@redhat.com> <20230713132306.GA13342@lorien.usersys.redhat.com> Date: Thu, 13 Jul 2023 13:12:04 -0700 In-Reply-To: <20230713132306.GA13342@lorien.usersys.redhat.com> (Phil Auld's message of "Thu, 13 Jul 2023 09:23:06 -0400") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/28.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Phil Auld writes: > On Wed, Jul 12, 2023 at 03:09:31PM -0700 Benjamin Segall wrote: >> Phil Auld writes: >> >> > In cgroupv2 cfs_b->hierarchical_quota is set to -1 for all task >> > groups due to the previous fix simply taking the min. It should >> > reflect a limit imposed at that level or by an ancestor. Even >> > though cgroupv2 does not require child quota to be less than or >> > equal to that of its ancestors the task group will still be >> > constrained by such a quota so this should be shown here. Cgroupv1 >> > continues to set this correctly. >> > >> > In both cases, add initialization when a new task group is created >> > based on the current parent's value (or RUNTIME_INF in the case of >> > root_task_group). Otherwise, the field is wrong until a quota is >> > changed after creation and __cfs_schedulable() is called. >> > >> > Fixes: c53593e5cb69 ("sched, cgroup: Don't reject lower cpu.max on ancestors") >> > Signed-off-by: Phil Auld >> > Reviewed-by: Ben Segall >> > Cc: Ingo Molnar >> > Cc: Peter Zijlstra >> > Cc: Vincent Guittot >> > Cc: Juri Lelli >> > Cc: Dietmar Eggemann >> > Cc: Valentin Schneider >> > Cc: Ben Segall >> > Cc: Frederic Weisbecker >> > Cc: Tejun Heo >> > --- >> > >> > v2: Improve comment about how setting hierarchical_quota correctly >> > >> > helps the scheduler. Remove extra parens. >> > kernel/sched/core.c | 13 +++++++++---- >> > kernel/sched/fair.c | 7 ++++--- >> > kernel/sched/sched.h | 2 +- >> > 3 files changed, 14 insertions(+), 8 deletions(-) >> > >> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c >> > index a68d1276bab0..f80697a79baf 100644 >> > --- a/kernel/sched/core.c >> > +++ b/kernel/sched/core.c >> > @@ -9904,7 +9904,7 @@ void __init sched_init(void) >> > ptr += nr_cpu_ids * sizeof(void **); >> > >> > root_task_group.shares = ROOT_TASK_GROUP_LOAD; >> > - init_cfs_bandwidth(&root_task_group.cfs_bandwidth); >> > + init_cfs_bandwidth(&root_task_group.cfs_bandwidth, NULL); >> > #endif /* CONFIG_FAIR_GROUP_SCHED */ >> > #ifdef CONFIG_RT_GROUP_SCHED >> > root_task_group.rt_se = (struct sched_rt_entity **)ptr; >> > @@ -11038,11 +11038,16 @@ static int tg_cfs_schedulable_down(struct task_group *tg, void *data) >> > >> > /* >> > * Ensure max(child_quota) <= parent_quota. On cgroup2, >> > - * always take the min. On cgroup1, only inherit when no >> > - * limit is set: >> > + * always take the non-RUNTIME_INF min. On cgroup1, only >> > + * inherit when no limit is set. In cgroup2 this is used >> > + * by the scheduler to determine if a given CFS task has a >> > + * bandwidth constraint at some higher level. >> > */ >> >> It's still used for determining this on cgroup1 (and the cgroup1 code >> still works for that), right? >> > > It would, except that the enforcement of child quota <= parent quota > means that cfs_rq->runtime_enabled will be set and we'll hit that first > on cgroup1. So we don't really use it for this determination in > cgroup1. cgroup1 tg_cfs_schedulable_down only constricts child quota when it's set. You can set quota=RUNTIME_INF on any cgroup, no matter what its parent is. (The schedulable constraint is a little silly)