Messages in this thread | | | Date | Thu, 3 Nov 2022 14:27:32 +0000 | From | Qais Yousef <> | Subject | Re: [PATCH v7 6/9] sched/fair: Add sched group latency support |
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On 11/03/22 09:46, Vincent Guittot wrote: > On Tue, 1 Nov 2022 at 20:28, Qais Yousef <qyousef@layalina.io> wrote: > > > > On 10/28/22 11:34, Vincent Guittot wrote: > > > Task can set its latency priority with sched_setattr(), which is then used > > > to set the latency offset of its sched_enity, but sched group entities > > > still have the default latency offset value. > > > > > > Add a latency.nice field in cpu cgroup controller to set the latency > > > priority of the group similarly to sched_setattr(). The latency priority > > > is then used to set the offset of the sched_entities of the group. > > > > > > Signed-off-by: Vincent Guittot <vincent.guittot@linaro.org> > > > --- > > > Documentation/admin-guide/cgroup-v2.rst | 8 ++++ > > > kernel/sched/core.c | 52 +++++++++++++++++++++++++ > > > kernel/sched/fair.c | 33 ++++++++++++++++ > > > kernel/sched/sched.h | 4 ++ > > > 4 files changed, 97 insertions(+) > > > > > > diff --git a/Documentation/admin-guide/cgroup-v2.rst b/Documentation/admin-guide/cgroup-v2.rst > > > index be4a77baf784..d8ae7e411f9c 100644 > > > --- a/Documentation/admin-guide/cgroup-v2.rst > > > +++ b/Documentation/admin-guide/cgroup-v2.rst > > > @@ -1095,6 +1095,14 @@ 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). > > > > I'm still not sure about this [1]. > > I'm still not sure about what you are trying to say here ... > > This is about setting a latency nice prio to a group level. > > > > > In some scenarios we'd like to get the effective latency_nice of the task. How > > will the task inherit the cgroup value or be impacted by it? > > > > For example if there are tasks that belong to a latency sensitive cgroup; and > > I'd like to skip some searches in EAS to improve that latency sensitivity - how > > would I extract this info in EAS path given these tasks are using default > > latency_nice value? And if should happen if their latency_nice is set to > > something else other than default? > > > > [1] https://lore.kernel.org/lkml/20221012160734.hrkb5jcjdq7r23pr@wubuntu/ > > Hmm so you are speaking about something that is not part of the patch. > Let focus on the patchset for now
I am focusing on this patchset. Isn't this an essential part of the design? Once the interface is out we can't change it. As it stands, I can't see how it can be used to replace prefer_idle in cgroup as used in Android. I can't see how this could happen if we don't define how the task will inherit the cgroup value. If we can, mind elaborating how please?
Thanks
-- Qais Yousef
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