From: Patrick Bellasi <patrick.bellasi@arm.com>
To: "Michal Koutný" <mkoutny@suse.com>
Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>, Tejun Heo <tj@kernel.org>,
"Rafael J . Wysocki" <rafael.j.wysocki@intel.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Viresh Kumar <viresh.kumar@linaro.org>,
Paul Turner <pjt@google.com>,
Quentin Perret <quentin.perret@arm.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Morten Rasmussen <morten.rasmussen@arm.com>,
Juri Lelli <juri.lelli@redhat.com>, Todd Kjos <tkjos@google.com>,
Joel Fernandes <joelaf@google.com>,
Steve Muckle <smuckle@google.com>,
Suren Baghdasaryan <surenb@google.com>,
Alessio Balsini <balsini@android.com>
Subject: Re: [PATCH v11 4/5] sched/core: uclamp: Use TG's clamps to restrict TASK's clamps
Date: Tue, 16 Jul 2019 15:34:35 +0100 [thread overview]
Message-ID: <20190716143435.iwwd6fjr3udlqol4@e110439-lin> (raw)
In-Reply-To: <20190715164248.GA21982@blackbody.suse.cz>
On 15-Jul 18:42, Michal Koutný wrote:
> On Mon, Jul 08, 2019 at 09:43:56AM +0100, Patrick Bellasi <patrick.bellasi@arm.com> wrote:
> > This mimics what already happens for a task's CPU affinity mask when the
> > task is also in a cpuset, i.e. cgroup attributes are always used to
> > restrict per-task attributes.
> If I am not mistaken when set_schedaffinity(2) call is made that results
> in an empty cpuset, the call fails with EINVAL [1].
>
> If I track the code correctly, the values passed to sched_setattr(2) are
> checked against the trivial validity (umin <= umax) and later on, they
> are adjusted to match the effective clamping of the containing
> task_group. Is that correct?
>
> If the user attempted to sched_setattr [a, b], and the effective uclamp
> was [c, d] such that [a, b] ∩ [c, d] = ∅, the set uclamp will be
> silently moved out of their intended range. Wouldn't it be better to
> return with EINVAL too when the intersection is empty (since the user
> supplied range won't be attained)?
You right for the cpuset case, but I don't think we never end up with
a "empty" set in the case of utilization clamping.
We limit clamps hierarchically in such a way that:
clamp[clamp_id] = min(task::clamp[clamp_id],
tg::clamp[clamp_id],
system::clamp[clamp_id])
and we ensure, on top of the above that:
clamp[UCLAMP_MIN] = min(clamp[UCLAMP_MIN], clamp[UCLAMP_MAX])
Since it's all and only about "capping" values, at the very extreme
case you can end up with:
clamp[UCLAMP_MIN] = clamp[UCLAMP_MAX] = 0
but that's till a valid configuration.
Am I missing something?
Otherwise, I think the changelog sentence you quoted is just
misleading. I'll remove it from v12 since it does not really clarify
anything more then the rest of the message.
Cheers,
Patrick
--
#include <best/regards.h>
Patrick Bellasi
next prev parent reply other threads:[~2019-07-16 14:34 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-08 8:43 [PATCH v11 0/5] Add utilization clamping support (CGroups API) Patrick Bellasi
2019-07-08 8:43 ` [PATCH v11 1/5] sched/core: uclamp: Extend CPU's cgroup controller Patrick Bellasi
2019-07-08 11:08 ` Quentin Perret
2019-07-15 13:38 ` Patrick Bellasi
2019-07-18 14:52 ` Tejun Heo
2019-07-18 15:26 ` Patrick Bellasi
2019-07-08 8:43 ` [PATCH v11 2/5] sched/core: uclamp: Propagate parent clamps Patrick Bellasi
2019-07-15 16:42 ` Michal Koutný
2019-07-16 14:07 ` Patrick Bellasi
2019-07-16 15:29 ` Michal Koutný
2019-07-16 17:55 ` Patrick Bellasi
2019-07-08 8:43 ` [PATCH v11 3/5] sched/core: uclamp: Propagate system defaults to root group Patrick Bellasi
2019-07-15 16:42 ` Michal Koutný
2019-07-16 14:34 ` Patrick Bellasi
2019-07-16 15:36 ` Michal Koutný
2019-07-16 18:00 ` Patrick Bellasi
2019-07-16 15:46 ` Joel Fernandes
2019-07-08 8:43 ` [PATCH v11 4/5] sched/core: uclamp: Use TG's clamps to restrict TASK's clamps Patrick Bellasi
2019-07-15 16:42 ` Michal Koutný
2019-07-16 14:34 ` Patrick Bellasi [this message]
2019-07-16 15:58 ` Michal Koutný
2019-07-08 8:43 ` [PATCH v11 5/5] sched/core: uclamp: Update CPU's refcount on TG's clamp changes Patrick Bellasi
2019-07-15 16:51 ` [PATCH v11 0/5] Add utilization clamping support (CGroups API) Michal Koutný
2019-07-16 14:03 ` Patrick Bellasi
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