From: Peter Zijlstra <peterz@infradead.org>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: songliubraving@fb.com, Ingo Molnar <mingo@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
tkjos@google.com, Daniel Lezcano <daniel.lezcano@linaro.org>,
quentin.perret@linaro.org, chris.redpath@arm.com,
Dietmar.Eggemann@arm.com, linux-kernel@vger.kernel.org,
steven.sistare@oracle.com
Subject: Re: [RFC V2 2/2] sched/fair: Fallback to sched-idle CPU if idle CPU isn't found
Date: Mon, 13 May 2019 13:35:18 +0200 [thread overview]
Message-ID: <20190513113518.GQ2623@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190513093418.altqhlhu4zsu75t4@vireshk-i7>
On Mon, May 13, 2019 at 03:04:18PM +0530, Viresh Kumar wrote:
> On 10-05-19, 09:21, Peter Zijlstra wrote:
> > I don't hate his per se; but the whole select_idle_sibling() thing is
> > something that needs looking at.
> >
> > There was the task stealing thing from Steve that looked interesting and
> > that would render your apporach unfeasible.
>
> I am surely missing something as I don't see how that patchset will
> make this patchset perform badly, than what it already does.
Nah; I just misremembered. I know Oracle has a patch set poking at
select_idle_siblings() _somewhere_ (as do I), and I just found the wrong
one.
Basically everybody is complaining select_idle_sibling() is too
expensive for checking the entire LLC domain, except for FB (and thus
likely some other workloads too) that depend on it to kill their tail
latency.
But I suppose we could still do this, even if we scan only a subset of
the LLC, just keep track of the last !idle CPU running only SCHED_IDLE
tasks and pick that if you do not (in your limited scan) find a better
candidate.
next prev parent reply other threads:[~2019-05-13 11:35 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-25 9:37 [RFC V2 0/2] sched/fair: Fallback to sched-idle CPU for better performance Viresh Kumar
2019-04-25 9:37 ` [RFC V2 1/2] sched: Start tracking SCHED_IDLE tasks count in cfs_rq Viresh Kumar
2019-05-10 6:55 ` Peter Zijlstra
2019-04-25 9:37 ` [RFC V2 2/2] sched/fair: Fallback to sched-idle CPU if idle CPU isn't found Viresh Kumar
2019-05-10 7:21 ` Peter Zijlstra
2019-05-13 9:34 ` Viresh Kumar
2019-05-13 11:35 ` Peter Zijlstra [this message]
2019-05-14 16:03 ` Steven Sistare
2019-05-14 17:27 ` Subhra Mazumdar
2019-05-14 17:36 ` Subhra Mazumdar
2019-06-04 2:58 ` Viresh Kumar
2019-05-09 21:54 ` [RFC V2 0/2] sched/fair: Fallback to sched-idle CPU for better performance Song Liu
2019-05-10 12:29 ` Vincent Guittot
2019-05-15 11:17 ` Viresh Kumar
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