From: Peter Zijlstra <peterz@infradead.org>
To: bsegall@google.com
Cc: Vincent Guittot <vincent.guittot@linaro.org>,
mingo@redhat.com, juri.lelli@redhat.com,
dietmar.eggemann@arm.com, rostedt@goodmis.org, mgorman@suse.de,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] sched/fair : prevent unlimited runtime on throttled group
Date: Mon, 20 Jan 2020 10:46:25 +0100 [thread overview]
Message-ID: <20200120094625.GL14879@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <xm26blr5oprc.fsf@bsegall-linux.svl.corp.google.com>
On Tue, Jan 14, 2020 at 10:29:43AM -0800, bsegall@google.com wrote:
> Vincent Guittot <vincent.guittot@linaro.org> writes:
>
> > When a running task is moved on a throttled task group and there is no
> > other task enqueued on the CPU, the task can keep running using 100% CPU
> > whatever the allocated bandwidth for the group and although its cfs rq is
> > throttled. Furthermore, the group entity of the cfs_rq and its parents are
> > not enqueued but only set as curr on their respective cfs_rqs.
> >
> > We have the following sequence:
> >
> > sched_move_task
> > -dequeue_task: dequeue task and group_entities.
> > -put_prev_task: put task and group entities.
> > -sched_change_group: move task to new group.
> > -enqueue_task: enqueue only task but not group entities because cfs_rq is
> > throttled.
> > -set_next_task : set task and group_entities as current sched_entity of
> > their cfs_rq.
> >
> > Another impact is that the root cfs_rq runnable_load_avg at root rq stays
> > null because the group_entities are not enqueued. This situation will stay
> > the same until an "external" event triggers a reschedule. Let trigger it
> > immediately instead.
>
> Sounds reasonable to me, "moved group" being an explicit resched check
> doesn't sound like a problem in general.
Do I read that as an Ack from you Ben? :-)
next prev parent reply other threads:[~2020-01-20 9:46 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-14 14:13 [PATCH] sched/fair : prevent unlimited runtime on throttled group Vincent Guittot
2020-01-14 18:29 ` bsegall
2020-01-20 9:46 ` Peter Zijlstra [this message]
2020-01-21 18:26 ` bsegall
2020-01-29 11:32 ` [tip: sched/core] sched/fair: Prevent " tip-bot2 for Vincent Guittot
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