Linux-PM Archive on lore.kernel.org
 help / color / Atom feed
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
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

  reply index

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

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20190625093144.g6forddrdql5lotv@e110439-lin \
    --to=patrick.bellasi@arm.com \
    --cc=balsini@android.com \
    --cc=dietmar.eggemann@arm.com \
    --cc=joelaf@google.com \
    --cc=juri.lelli@redhat.com \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-pm@vger.kernel.org \
    --cc=mingo@redhat.com \
    --cc=morten.rasmussen@arm.com \
    --cc=peterz@infradead.org \
    --cc=pjt@google.com \
    --cc=quentin.perret@arm.com \
    --cc=rafael.j.wysocki@intel.com \
    --cc=smuckle@google.com \
    --cc=surenb@google.com \
    --cc=tj@kernel.org \
    --cc=tkjos@google.com \
    --cc=vincent.guittot@linaro.org \
    --cc=viresh.kumar@linaro.org \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-PM Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-pm/0 linux-pm/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-pm linux-pm/ https://lore.kernel.org/linux-pm \
		linux-pm@vger.kernel.org
	public-inbox-index linux-pm

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-pm


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git