From: Juri Lelli <juri.lelli@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Vincent Guittot <vincent.guittot@linaro.org>,
mingo@kernel.org, linux-kernel@vger.kernel.org,
rjw@rjwysocki.net, dietmar.eggemann@arm.com,
Morten.Rasmussen@arm.com
Subject: Re: [RFC PATCH 1/2] sched/rt: add utilization tracking
Date: Wed, 31 May 2017 11:41:11 +0100 [thread overview]
Message-ID: <20170531104111.cep53srg5r3ldmh5@e106622-lin> (raw)
In-Reply-To: <20170531103017.3voouif2ixwbpbyn@hirez.programming.kicks-ass.net>
On 31/05/17 12:30, Peter Zijlstra wrote:
> On Wed, May 31, 2017 at 11:40:47AM +0200, Peter Zijlstra wrote:
> > On Wed, May 24, 2017 at 11:00:51AM +0200, Vincent Guittot wrote:
> > > schedutil governor relies on cfs_rq's util_avg to choose the OPP when cfs
> > > tasks are running. When the CPU is overloaded by cfs and rt tasks, cfs tasks
> > > are preempted by rt tasks and in this case util_avg reflects the remaining
> > > capacity that is used by cfs tasks but not what cfs tasks want to use. In such
> > > case, schedutil can select a lower OPP when cfs task runs whereas the CPU is
> > > overloaded. In order to have a more accurate view of the utilization of the
> > > CPU, we track the utilization that is used by RT tasks.
> > > DL tasks are not taken into account as they have their own utilization
> > > tracking mecanism.
> >
> > Well, the DL tracking is fairly pessimistic; it assumes all DL tasks
> > will consume their total budget, which will rarely, if ever, happen.
> >
> > So I suspect it might well be worth it to also track DL activity for the
> > purpose of compensating CFS.
>
> Again, it seems I have this CPPC/HWP crud firmly stuck in my brain.
> Because I was thinking:
>
> min_freq = dl_util
> avg_freq = dl_avg + rt_avg + cfs_util
>
>
> But given we don't actually have that split... meh.
>
Right, interesting. So, I guess the question is: should we have it? :)
IMHO, it makes sense and seems to benefit mobile use-cases I'm looking
at.
rt_avg though it also seems to build up very slowly (at least with
default configs). I'm experimenting with Vincent proposal and it looks
better (w.r.t. using rt_avg). Also summing up signals that behave
similarly doesn't seem the wrong thing to do.
next prev parent reply other threads:[~2017-05-31 10:41 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-05-24 9:00 [PATCH 0/2] track rt rq utilization Vincent Guittot
2017-05-24 9:00 ` [RFC PATCH 1/2] sched/rt: add utilization tracking Vincent Guittot
2017-05-30 15:50 ` Morten Rasmussen
2017-05-30 16:24 ` Vincent Guittot
2017-05-31 7:57 ` Morten Rasmussen
2017-05-31 9:40 ` Peter Zijlstra
2017-05-31 10:30 ` Peter Zijlstra
2017-05-31 10:41 ` Juri Lelli [this message]
2017-05-31 11:39 ` Peter Zijlstra
2017-05-31 11:24 ` Vincent Guittot
2017-05-24 9:00 ` [PATCH 2/2] cpufreq/schedutil: add rt " Vincent Guittot
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