LKML Archive on lore.kernel.org
 help / color / Atom feed
From: Suren Baghdasaryan <surenb@google.com>
To: Patrick Bellasi <patrick.bellasi@arm.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>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Paul Turner <pjt@google.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>
Subject: Re: [PATCH v2 10/12] sched/core: uclamp: use TG's clamps to restrict Task's clamps
Date: Tue, 24 Jul 2018 08:28:41 -0700
Message-ID: <CAJuCfpEUsq=LPZgz20jn79CwymQGgfif8j8fzurUDmEJ3G9q5w@mail.gmail.com> (raw)
In-Reply-To: <20180724095550.GA3162@e110439-lin>

Hi Patrick. Thanks for the explanation and links. No more questions
from me on this one :)

On Tue, Jul 24, 2018 at 2:56 AM, Patrick Bellasi
<patrick.bellasi@arm.com> wrote:
> On 23-Jul 10:11, Suren Baghdasaryan wrote:
>> On Mon, Jul 23, 2018 at 8:40 AM, Patrick Bellasi
>> <patrick.bellasi@arm.com> wrote:
>> > On 21-Jul 20:05, Suren Baghdasaryan wrote:
>> >> On Mon, Jul 16, 2018 at 1:29 AM, Patrick Bellasi
>
> [...]
>
>> >> So to satisfy both TG and syscall requirements I think you would
>> >> need to choose the largest value for UCLAMP_MIN and the smallest one
>> >> for UCLAMP_MAX, meaning the most boosted and most clamped range.
>> >> Current implementation choses the least boosted value, so
>> >> effectively one of the UCLAMP_MIN requirements (either from TG or
>> >> from syscall) are being ignored...  Could you please clarify why
>> >> this choice is made?
>> >
>> > The TG values are always used to specify a _restriction_ on
>> > task-specific values.
>> >
>> > Thus, if you look or example at the CPU mask for a task, you can have
>> > a task with affinity to CPUs 0-1, currently running on a cgroup with
>> > cpuset.cpus=0... then the task can run only on CPU 0 (althought its
>> > affinity includes CPU1 too).
>> >
>> > Same we do here: if a task has util_min=10, but it's running in a
>> > cgroup with cpu.util_min=0, then it will not be boosted.
>> >
>> > IOW, this allows to implement a "nice" policy at task level, where a
>> > task (via syscall) can decide to be less boosted with respect to its
>> > group but never more boosted. The same task can also decide to be more
>> > clamped, but not less clamped then its current group.
>> >
>>
>> The fact that boost means "at least this much" to me seems like we can
>> safely choose higher CPU bandwidth (as long as it's lower than
>> UCLAMP_MAX)
>
> I understand your view point, which actually is matching my first
> implementation for util_min aggregation:
>
>    https://lore.kernel.org/lkml/20180409165615.2326-5-patrick.bellasi@arm.com/
>
>
>> but from your description sounds like TG's UCLAMP_MIN means "at most
>> this much boost" and it's not safe to use CPU bandwidth higher than
>> TG's UCLAMP_MIN.
>
> Indeed, after this discussion with Tejun:
>
>    https://lore.kernel.org/lkml/20180409222417.GK3126663@devbig577.frc2.facebook.com/
>
> I've convinced myself that for the cgroup interface we have to got for
> a "restrictive" interface where a parent value must set the upper
> bound for all its descendants values. AFAIU, that's one of the basic
> principles of the "delegation model" implemented by cgroups and the
> common behavior implemented by all controllers.
>
>> So instead of specifying min CPU bandwidth for a task it specifies
>> the max allowed boost. Seems like a discrepancy to me but maybe
>> there are compelling usecases when this behavior is necessary?
>
> I don't think it's strictly related to use-cases, you can always
> describe a give use-case in one model or the other.  It all depends on
> how you configure your hierarchy and where you place your tasks.
>
> For our Android use cases, we are still happy to say that all tasks of
> a CGroup can be boosted up to a certain value and then we can either:
> - don't configure tasks: and thus get the CG defined boost
> - configure a task: and explicitly give back what we don't need
>
> This model works quite well with containers, where the parent want to
> precisely control how much resources are (eventually) usable by a
> given container.
>
>> In that case would be good to spell them out to explain why this
>> choice is made.
>
> Yes, well... if I understand it correctly is really just the
> recommended way cgroups must be used to re-partition resources.
>
> I'll try to better explain this behavior in the changelog for this
> patch.
>
> [...]
>
> Best,
> Patrick
>
> --
> #include <best/regards.h>
>
> Patrick Bellasi

  reply index

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-07-16  8:28 [PATCH v2 00/12] Add utilization clamping support Patrick Bellasi
2018-07-16  8:28 ` [PATCH v2 01/12] sched/core: uclamp: extend sched_setattr to support utilization clamping Patrick Bellasi
2018-07-17 17:50   ` Joel Fernandes
2018-07-18  8:42     ` Patrick Bellasi
2018-07-18 17:02       ` Joel Fernandes
2018-07-17 18:04   ` Joel Fernandes
2018-07-16  8:28 ` [PATCH v2 02/12] sched/core: uclamp: map TASK's clamp values into CPU's clamp groups Patrick Bellasi
2018-07-19 23:51   ` Suren Baghdasaryan
2018-07-20 15:11     ` Patrick Bellasi
2018-07-21  0:25       ` Suren Baghdasaryan
2018-07-23 13:36         ` Patrick Bellasi
2018-07-16  8:28 ` [PATCH v2 03/12] sched/core: uclamp: add CPU's clamp groups accounting Patrick Bellasi
2018-07-20 20:25   ` Suren Baghdasaryan
2018-07-16  8:28 ` [PATCH v2 04/12] sched/core: uclamp: update CPU's refcount on clamp changes Patrick Bellasi
2018-07-16  8:28 ` [PATCH v2 05/12] sched/cpufreq: uclamp: add utilization clamping for FAIR tasks Patrick Bellasi
2018-07-16  8:29 ` [PATCH v2 06/12] sched/cpufreq: uclamp: add utilization clamping for RT tasks Patrick Bellasi
2018-07-16  8:29 ` [PATCH v2 07/12] sched/core: uclamp: enforce last task UCLAMP_MAX Patrick Bellasi
2018-07-21  1:23   ` Suren Baghdasaryan
2018-07-23 15:02     ` Patrick Bellasi
2018-07-23 16:40       ` Suren Baghdasaryan
2018-07-16  8:29 ` [PATCH v2 08/12] sched/core: uclamp: extend cpu's cgroup controller Patrick Bellasi
2018-07-21  2:37   ` Suren Baghdasaryan
2018-07-21  3:16     ` Suren Baghdasaryan
2018-07-23 15:17     ` Patrick Bellasi
2018-07-23 15:30   ` Tejun Heo
2018-07-23 17:22     ` Patrick Bellasi
2018-07-24 13:29       ` Tejun Heo
2018-07-24 15:39         ` Patrick Bellasi
2018-07-27  0:39         ` Joel Fernandes
2018-07-27  8:09           ` Quentin Perret
2018-07-16  8:29 ` [PATCH v2 09/12] sched/core: uclamp: map TG's clamp values into CPU's clamp groups Patrick Bellasi
2018-07-16  8:29 ` [PATCH v2 10/12] sched/core: uclamp: use TG's clamps to restrict Task's clamps Patrick Bellasi
2018-07-22  3:05   ` Suren Baghdasaryan
2018-07-23 15:40     ` Patrick Bellasi
2018-07-23 17:11       ` Suren Baghdasaryan
2018-07-24  9:56         ` Patrick Bellasi
2018-07-24 15:28           ` Suren Baghdasaryan [this message]
2018-07-24 15:49             ` Patrick Bellasi
2018-07-16  8:29 ` [PATCH v2 11/12] sched/core: uclamp: update CPU's refcount on TG's clamp changes Patrick Bellasi
2018-07-22  3:17   ` Suren Baghdasaryan
2018-07-16  8:29 ` [PATCH v2 12/12] sched/core: uclamp: use percentage clamp values Patrick Bellasi
2018-07-22  4:04   ` Suren Baghdasaryan
2018-07-24 16:43     ` Patrick Bellasi
2018-07-24 17:11       ` Suren Baghdasaryan
2018-07-24 17:17         ` Patrick Bellasi
2018-07-17 13:03 ` [PATCH v2 00/12] Add utilization clamping support Joel Fernandes
2018-07-17 13:41   ` Patrick Bellasi

Reply instructions:

You may reply publicly 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='CAJuCfpEUsq=LPZgz20jn79CwymQGgfif8j8fzurUDmEJ3G9q5w@mail.gmail.com' \
    --to=surenb@google.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=patrick.bellasi@arm.com \
    --cc=peterz@infradead.org \
    --cc=pjt@google.com \
    --cc=rafael.j.wysocki@intel.com \
    --cc=smuckle@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

LKML Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/lkml/0 lkml/git/0.git
	git clone --mirror https://lore.kernel.org/lkml/1 lkml/git/1.git
	git clone --mirror https://lore.kernel.org/lkml/2 lkml/git/2.git
	git clone --mirror https://lore.kernel.org/lkml/3 lkml/git/3.git
	git clone --mirror https://lore.kernel.org/lkml/4 lkml/git/4.git
	git clone --mirror https://lore.kernel.org/lkml/5 lkml/git/5.git
	git clone --mirror https://lore.kernel.org/lkml/6 lkml/git/6.git
	git clone --mirror https://lore.kernel.org/lkml/7 lkml/git/7.git
	git clone --mirror https://lore.kernel.org/lkml/8 lkml/git/8.git
	git clone --mirror https://lore.kernel.org/lkml/9 lkml/git/9.git

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

Example config snippet for mirrors

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


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