From: Patrick Bellasi <patrick.bellasi@arm.com>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Juri Lelli <juri.lelli@redhat.com>,
linux-kernel <linux-kernel@vger.kernel.org>,
"open list:THERMAL" <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>,
Paul Turner <pjt@google.com>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Morten Rasmussen <morten.rasmussen@arm.com>,
Todd Kjos <tkjos@google.com>, Joel Fernandes <joelaf@google.com>,
"Cc: Steve Muckle" <smuckle@google.com>,
surenb@google.com
Subject: Re: [PATCH v3 06/14] sched/cpufreq: uclamp: add utilization clamping for RT tasks
Date: Mon, 13 Aug 2018 11:12:21 +0100 [thread overview]
Message-ID: <20180813101221.GA2605@e110439-lin> (raw)
In-Reply-To: <CAKfTPtCWcq2bOmaC5EDdhS8ih8Sv7Mwzn=84xerKA2tY6kXLkw@mail.gmail.com>
Hi Vincent!
On 09-Aug 18:03, Vincent Guittot wrote:
> > On 07-Aug 15:26, Juri Lelli wrote:
[...]
> > > > + util_cfs = cpu_util_cfs(rq);
> > > > + util_rt = cpu_util_rt(rq);
> > > > + if (sched_feat(UCLAMP_SCHED_CLASS)) {
> > > > + util = 0;
> > > > + if (util_cfs)
> > > > + util += uclamp_util(cpu_of(rq), util_cfs);
> > > > + if (util_rt)
> > > > + util += uclamp_util(cpu_of(rq), util_rt);
> > > > + } else {
> > > > + util = cpu_util_cfs(rq);
> > > > + util += cpu_util_rt(rq);
> > > > + util = uclamp_util(cpu_of(rq), util);
> > > > + }
> >
> > Regarding the two policies, do you have any comment?
>
> Does the policy for (sched_feat(UCLAMP_SCHED_CLASS)== true) really
> make sense as it is ?
> I mean, uclamp_util doesn't make any difference between rt and cfs
> tasks when clamping the utilization so why should be add twice the
> returned value ?
> IMHO, this policy would make sense if there were something like
> uclamp_util_rt() and a uclamp_util_cfs()
The idea for the UCLAMP_SCHED_CLASS policy is to improve fairness on
low-priority classese, especially when we have high RT utilization.
Let say we have:
util_rt = 40%, util_min=0%
util_cfs = 10%, util_min=50%
the two policies will select:
UCLAMP_SCHED_CLASS: util = uclamp(40) + uclamp(10) = 50 + 50 = 100%
!UCLAMP_SCHED_CLASS: util = uclamp(40 + 10) = uclmp(50) = 50%
Which means that, despite the CPU's util_min will be set to 50% when
CFS is running, these tasks will have almost no boost at all, since
their bandwidth margin is eclipsed by RT tasks.
> > We had an internal discussion and we found pro/cons for both... but
The UCLAMP_SCHED_CLASS policy is thus less energy efficiency but it
should grant a better "isolation" in terms of what is the expected
speed-up a task will get at run-time, independently from higher
priority classes.
Does that make sense?
> > I'm not sure keeping the sched_feat is a good solution on the long
> > run, i.e. mainline merge ;)
This problem still stands...
--
#include <best/regards.h>
Patrick Bellasi
next prev parent reply other threads:[~2018-08-13 10:12 UTC|newest]
Thread overview: 82+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-08-06 16:39 [PATCH v3 00/14] Add utilization clamping support Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 01/14] sched/core: uclamp: extend sched_setattr to support utilization clamping Patrick Bellasi
2018-08-06 16:50 ` Randy Dunlap
2018-08-09 8:39 ` Patrick Bellasi
2018-08-09 15:20 ` Randy Dunlap
2018-08-07 9:59 ` Juri Lelli
2018-08-13 12:14 ` Patrick Bellasi
2018-08-13 12:27 ` Juri Lelli
2018-08-07 12:35 ` Juri Lelli
2018-08-09 9:14 ` Patrick Bellasi
2018-08-09 9:50 ` Juri Lelli
2018-08-09 15:23 ` Patrick Bellasi
2018-08-10 7:50 ` Juri Lelli
2018-08-17 10:34 ` Quentin Perret
2018-08-17 10:57 ` Patrick Bellasi
2018-08-17 11:14 ` Quentin Perret
2018-08-06 16:39 ` [PATCH v3 02/14] sched/core: uclamp: map TASK's clamp values into CPU's clamp groups Patrick Bellasi
2018-08-14 11:25 ` Pavan Kondeti
2018-08-14 15:21 ` Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 03/14] sched/core: uclamp: add CPU's clamp groups accounting Patrick Bellasi
2018-08-14 15:44 ` Dietmar Eggemann
2018-08-14 16:49 ` Patrick Bellasi
2018-08-15 9:37 ` Dietmar Eggemann
2018-08-15 10:54 ` Patrick Bellasi
2018-08-15 10:59 ` Dietmar Eggemann
2018-08-16 13:32 ` Patrick Bellasi
2018-08-16 13:37 ` Quentin Perret
2018-08-16 13:45 ` Dietmar Eggemann
2018-08-16 14:21 ` Quentin Perret
2018-08-16 15:00 ` Dietmar Eggemann
2018-08-17 11:04 ` Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 04/14] sched/core: uclamp: update CPU's refcount on clamp changes Patrick Bellasi
2018-08-15 15:02 ` Dietmar Eggemann
2018-08-16 13:22 ` Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 05/14] sched/cpufreq: uclamp: add utilization clamping for FAIR tasks Patrick Bellasi
2018-08-08 13:18 ` Vincent Guittot
2018-08-09 15:30 ` Patrick Bellasi
2018-08-15 15:30 ` Dietmar Eggemann
2018-08-16 13:53 ` Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 06/14] sched/cpufreq: uclamp: add utilization clamping for RT tasks Patrick Bellasi
2018-08-07 13:26 ` Juri Lelli
2018-08-09 15:34 ` Patrick Bellasi
2018-08-09 16:03 ` Vincent Guittot
2018-08-13 10:12 ` Patrick Bellasi [this message]
2018-08-13 10:50 ` Juri Lelli
2018-08-13 12:07 ` Vincent Guittot
2018-08-13 12:09 ` Vincent Guittot
2018-08-13 12:49 ` Patrick Bellasi
2018-08-13 14:06 ` Vincent Guittot
2018-08-13 15:01 ` Patrick Bellasi
2018-08-16 10:34 ` Dietmar Eggemann
2018-08-16 13:40 ` Patrick Bellasi
2018-08-07 13:54 ` Quentin Perret
2018-08-09 15:41 ` Patrick Bellasi
2018-08-09 15:55 ` Quentin Perret
2018-08-13 10:17 ` Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 07/14] sched/core: uclamp: enforce last task UCLAMP_MAX Patrick Bellasi
2018-08-16 15:43 ` Dietmar Eggemann
2018-08-16 16:47 ` Patrick Bellasi
2018-08-16 17:10 ` Dietmar Eggemann
2018-08-16 17:27 ` Patrick Bellasi
2018-08-16 17:20 ` Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 08/14] sched/core: uclamp: extend cpu's cgroup controller Patrick Bellasi
2018-08-17 12:21 ` Dietmar Eggemann
2018-08-17 14:24 ` Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 09/14] sched/core: uclamp: propagate parent clamps Patrick Bellasi
2018-08-16 9:09 ` Pavan Kondeti
2018-08-16 14:07 ` Patrick Bellasi
2018-08-17 13:43 ` Dietmar Eggemann
2018-08-17 14:45 ` Patrick Bellasi
2018-08-17 15:50 ` Dietmar Eggemann
2018-08-20 10:01 ` Dietmar Eggemann
2018-08-20 12:28 ` Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 10/14] sched/core: uclamp: map TG's clamp values into CPU's clamp groups Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 11/14] sched/core: uclamp: use TG's clamps to restrict Task's clamps Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 12/14] sched/core: uclamp: add system default clamps Patrick Bellasi
2018-08-16 9:13 ` Pavan Kondeti
2018-08-16 14:37 ` Patrick Bellasi
2018-08-20 10:18 ` Dietmar Eggemann
2018-08-20 12:27 ` Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 13/14] sched/core: uclamp: update CPU's refcount on TG's clamp changes Patrick Bellasi
2018-08-06 16:39 ` [PATCH v3 14/14] sched/core: uclamp: use percentage clamp values Patrick Bellasi
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