[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <CAKfTPtDiKF7x0obCFXmNsmJdsJ9yXzAf4vuOVJmN_eO_bA8KHQ@mail.gmail.com>
Date: Mon, 14 Nov 2022 17:57:30 +0100
From: Vincent Guittot <vincent.guittot@...aro.org>
To: Patrick Bellasi <patrick.bellasi@...bug.net>
Cc: mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
dietmar.eggemann@....com, rostedt@...dmis.org, bsegall@...gle.com,
mgorman@...e.de, bristot@...hat.com, vschneid@...hat.com,
linux-kernel@...r.kernel.org, parth@...ux.ibm.com,
qyousef@...alina.io, chris.hyser@...cle.com,
David.Laight@...lab.com, pjt@...gle.com, pavel@....cz,
tj@...nel.org, qperret@...gle.com, tim.c.chen@...ux.intel.com,
joshdon@...gle.com, timj@....org, kprateek.nayak@....com,
yu.c.chen@...el.com, youssefesmat@...omium.org,
joel@...lfernandes.org
Subject: Re: [PATCH v8 6/9] sched/fair: Add sched group latency support
On Mon, 14 Nov 2022 at 17:20, Patrick Bellasi
<patrick.bellasi@...bug.net> wrote:
>
> Hi Vincent,
>
> On 10-Nov 18:50, Vincent Guittot wrote:
>
> [...]
>
> > diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst
> > index be4a77baf784..a4866cd4e58c 100644
> > --- a/Documentation/admin-guide/cgroup-v2.rst
> > +++ b/Documentation/admin-guide/cgroup-v2.rst
> > @@ -1095,6 +1095,16 @@ All time durations are in microseconds.
> > values similar to the sched_setattr(2). This maximum utilization
> > value is used to clamp the task specific maximum utilization clamp.
> >
> > + cpu.latency.nice
> > + A read-write single value file which exists on non-root
> > + cgroups. The default is "0".
> > +
> > + The nice value is in the range [-20, 19].
> > +
> > + This interface file allows reading and setting latency using the
> > + same values used by sched_setattr(2). The latency_nice of a group is
> > + used to limit the impact of the latency_nice of a task outside the
> > + group.
>
> This control model is not clear to me.
>
> It does not seem matching what we have for uclamp, where the cgroup values are
> used to restrict how much a task can ask or give (in terms of latency here).
>
> in the uclamp's requested-vs-effective values model:
>
> A) a task can "request" (or give up) latency as much as it likes
>
> B) the cgroup in which the task is in any moment limits wthe maximum
> latency a task can "request" (or give up)
>
> C) the system wide knob set the "request" limit for the root cgroup an any task
> not in a cgroup.
>
> This model seems to be what we should use here too.
>
> IOW, for each task compute an "effective" latency_nice value which is defined
> starting for a task "requested" latency value and by restricting this value
> based on the (B) cgroup value and the (C) system wide value.
>
> That's what we do in uclamp_eff_get():
> https://elixir.bootlin.com/linux/v6.0/source/kernel/sched/core.c#L1484
>
> Why such a model cannot be used for latency_nice too?
> Am I missing something?
Have you read the previous email thread on the subject ?
As I mentioned previously we don't need an effective latency for this
patchset because the current use of cgroup latency_nice is done at
each scheduling level just like the cgroup weight is used at each
level.
Regards,
Vincent
>
>
> Best,
> patrick
>
> --
> #include <best/regards.h>
>
> Patrick Bellasi
Powered by blists - more mailing lists