From: Patrick Bellasi <patrick.bellasi@arm.com>
To: Tejun Heo <tj@kernel.org>
Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.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 v10 12/16] sched/core: uclamp: Extend CPU's cgroup controller
Date: Tue, 25 Jun 2019 10:31:44 +0100 [thread overview]
Message-ID: <20190625093144.g6forddrdql5lotv@e110439-lin> (raw)
In-Reply-To: <20190624175215.GR657710@devbig004.ftw2.facebook.com>
On 24-Jun 10:52, Tejun Heo wrote:
> Hey, Patrick.
Hi,
> On Mon, Jun 24, 2019 at 06:29:06PM +0100, Patrick Bellasi wrote:
> > > I kinda wonder whether the term bandwidth is a bit confusing because
> > > it's also used for cpu.max/min. Would just calling it frequency be
> > > clearer?
> >
> > Maybe I should find a better way to express the concept above.
> >
> > I agree that bandwidth is already used by cpu.{max,min}, what I want
> > to call out is that clamps allows to enrich that concept.
> >
> > By hinting the scheduler on min/max required utilization we can better
> > defined the amount of actual CPU cycles required/allowed.
> > That's a bit more precise bandwidth control compared to just rely on
> > temporal runnable/period limits.
>
> I see. I wonder whether it's overloading the same term too subtly
> tho. It's great to document how they interact but it *might* be
> easier for readers if a different term is used even if the meaning is
> essentially the same. Anyways, it's a nitpick. Please feel free to
> ignore.
Got it, will try come up with a better description in the v11 to avoid
confusion and better explain the "improvements" without polluting too
much the original concept.
> > > > + tg = css_tg(of_css(of));
> > > > + if (tg == &root_task_group) {
> > > > + ret = -EINVAL;
> > > > + goto out;
> > > > + }
> > >
> > > I don't think you need the above check.
> >
> > Don't we want to forbid attributes tuning from the root group?
>
> Yeah, that's enforced by NOT_ON_ROOT flag, right?
Oh right, since we don't show them we can't write them :)
> > > So, uclamp.max limits the maximum freq% can get and uclamp.min limits
> > > hte maximum freq% protection can get in the subtree. Let's say
> > > uclamp.max is 50% and uclamp.min is 100%.
> >
> > That's not possible, in the current implementation we always enforce
> > the limit (uclamp.max) to be _not smaller_ then the protection
> > (uclamp.min).
> >
> > Indeed, in principle, it does not make sense to ask for a minimum
> > utilization (i.e. frequency boosting) which is higher then the
> > maximum allowed utilization (i.e. frequency capping).
>
> Yeah, I'm trying to explain actually it does.
>
> > > It means that protection is not limited but the actual freq% is
> > > limited upto 50%, which isn't necessarily invalid.
> > > For a simple example, a user might be saying
> > > that they want to get whatever protection they can get from its parent
> > > but wanna limit eventual freq at 50% and it isn't too difficult to
> > > imagine cases where the two knobs are configured separately especially
> > > configuration is being managed hierarchically / automatically.
> >
> > That's not my understanding, in v10 by default when we create a
> > subgroup we assign it uclamp.min=0%, meaning that we don't boost
> > frequencies.
> >
> > It seems instead that you are asking to set uclamp.min=100% by
> > default, so that the effective value will give us whatever the father
> > allow. Is that correct?
>
> No, the defaults are fine. I'm trying to say that min/max
> configurations don't need to be coupled like this and there are valid
> use cases where the configured min is higher than max when
> configurations are nested and managed automatically.
>
> Limits always trump protection in effect of course but please don't
> limit what can be configured.
Got it, thanks!
Will fix it in v11.
> Thanks.
>
> --
> tejun
Cheers,
Patrick
--
#include <best/regards.h>
Patrick Bellasi
next prev parent reply other threads:[~2019-06-25 9:31 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-21 8:42 [PATCH v10 00/16] Add utilization clamping support Patrick Bellasi
2019-06-21 8:42 ` [PATCH v10 01/16] sched/core: uclamp: Add CPU's clamp buckets refcounting Patrick Bellasi
2019-06-21 8:42 ` [PATCH v10 02/16] sched/core: uclamp: Add bucket local max tracking Patrick Bellasi
2019-06-21 8:42 ` [PATCH v10 03/16] sched/core: uclamp: Enforce last task's UCLAMP_MAX Patrick Bellasi
2019-06-21 8:42 ` [PATCH v10 04/16] sched/core: uclamp: Add system default clamps Patrick Bellasi
2019-06-21 8:42 ` [PATCH v10 05/16] sched/core: Allow sched_setattr() to use the current policy Patrick Bellasi
2019-06-21 8:42 ` [PATCH v10 06/16] sched/core: uclamp: Extend sched_setattr() to support utilization clamping Patrick Bellasi
2019-06-21 8:42 ` [PATCH v10 07/16] sched/core: uclamp: Reset uclamp values on RESET_ON_FORK Patrick Bellasi
2019-06-21 8:42 ` [PATCH v10 08/16] sched/core: uclamp: Set default clamps for RT tasks Patrick Bellasi
2019-06-21 8:42 ` [PATCH v10 09/16] sched/cpufreq: uclamp: Add clamps for FAIR and " Patrick Bellasi
2019-06-21 8:42 ` [PATCH v10 10/16] sched/core: uclamp: Add uclamp_util_with() Patrick Bellasi
2019-06-21 8:42 ` [PATCH v10 11/16] sched/fair: uclamp: Add uclamp support to energy_compute() Patrick Bellasi
2019-06-21 14:01 ` Peter Zijlstra
2019-06-21 14:47 ` Patrick Bellasi
2019-06-21 8:42 ` [PATCH v10 12/16] sched/core: uclamp: Extend CPU's cgroup controller Patrick Bellasi
2019-06-22 15:03 ` Tejun Heo
2019-06-24 17:29 ` Patrick Bellasi
2019-06-24 17:52 ` Tejun Heo
2019-06-25 9:31 ` Patrick Bellasi [this message]
2019-06-21 8:42 ` [PATCH v10 13/16] sched/core: uclamp: Propagate parent clamps Patrick Bellasi
2019-06-22 15:07 ` Tejun Heo
2019-06-24 17:34 ` Patrick Bellasi
2019-06-24 17:46 ` Tejun Heo
2019-06-21 8:42 ` [PATCH v10 14/16] sched/core: uclamp: Propagate system defaults to root group Patrick Bellasi
2019-06-21 8:42 ` [PATCH v10 15/16] sched/core: uclamp: Use TG's clamps to restrict TASK's clamps Patrick Bellasi
2019-06-21 8:42 ` [PATCH v10 16/16] sched/core: uclamp: Update CPU's refcount on TG's clamp changes Patrick Bellasi
2019-06-21 14:55 ` [PATCH v10 00/16] Add utilization clamping support Patrick Bellasi
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