From: Patrick Bellasi <patrick.bellasi@arm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
Ingo Molnar <mingo@redhat.com>, 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>,
Joel Fernandes <joelaf@google.com>,
Steve Muckle <smuckle@google.com>
Subject: Re: [PATCH 1/7] sched/core: uclamp: add CPU clamp groups accounting
Date: Fri, 13 Apr 2018 12:08:48 +0100 [thread overview]
Message-ID: <20180413110848.GR14248@e110439-lin> (raw)
In-Reply-To: <20180413094615.GT4043@hirez.programming.kicks-ass.net>
On 13-Apr 11:46, Peter Zijlstra wrote:
> On Mon, Apr 09, 2018 at 05:56:09PM +0100, Patrick Bellasi wrote:
> > +static inline void uclamp_cpu_get(struct task_struct *p, int cpu, int clamp_id)
> > +{
> > + struct uclamp_cpu *uc_cpu = &cpu_rq(cpu)->uclamp[clamp_id];
> > + int clamp_value;
> > + int group_id;
> > +
> > + /* Get task's specific clamp value */
> > + clamp_value = p->uclamp[clamp_id].value;
> > + group_id = p->uclamp[clamp_id].group_id;
> > +
> > + /* No task specific clamp values: nothing to do */
> > + if (group_id == UCLAMP_NONE)
> > + return;
> > +
> > + /* Increment the current group_id */
>
> That I think qualifies being called a bad comment.
my bad :/
> > + uc_cpu->group[group_id].tasks += 1;
> > +
> > + /* Mark task as enqueued for this clamp index */
> > + p->uclamp_group_id[clamp_id] = group_id;
>
> Why exactly do we need this? we got group_id from @p in the first place.
The idea is to back-annotate on the task the group in which it has
been refcounted. That allows a much simpler and less racy refcount
decrements at dequeue/migration time.
That's also why we have a single call-back, uclamp_task_update(),
for both enqueue/dequeue. Depending on the check performed by
uclamp_task_affects() we know if we have to get or put the refcounter.
> I suspect this is because when we update p->uclamp[], we don't update
> this active value (when needed), is that worth it?
What you mean by "we don't update this active value"?
> > + /*
> > + * If this is the new max utilization clamp value, then we can update
> > + * straight away the CPU clamp value. Otherwise, the current CPU clamp
> > + * value is still valid and we are done.
> > + */
> > + if (uc_cpu->value < clamp_value)
> > + uc_cpu->value = clamp_value;
> > +}
--
#include <best/regards.h>
Patrick Bellasi
next prev parent reply other threads:[~2018-04-13 11:08 UTC|newest]
Thread overview: 32+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-04-09 16:56 [PATCH 0/7] Add utilization clamping support Patrick Bellasi
2018-04-09 16:56 ` [PATCH 1/7] sched/core: uclamp: add CPU clamp groups accounting Patrick Bellasi
2018-04-13 8:26 ` Peter Zijlstra
2018-04-13 10:22 ` Peter Zijlstra
2018-04-13 11:04 ` Patrick Bellasi
2018-04-13 11:15 ` Peter Zijlstra
2018-04-13 8:40 ` Peter Zijlstra
2018-04-13 11:17 ` Patrick Bellasi
2018-04-13 11:29 ` Peter Zijlstra
2018-04-13 11:33 ` Patrick Bellasi
2018-04-13 8:43 ` Peter Zijlstra
2018-04-13 11:15 ` Patrick Bellasi
2018-04-13 11:36 ` Peter Zijlstra
2018-04-13 11:47 ` Patrick Bellasi
2018-04-13 11:52 ` Patrick Bellasi
2018-04-13 12:44 ` Peter Zijlstra
2018-04-13 9:30 ` Peter Zijlstra
2018-04-13 9:38 ` Peter Zijlstra
2018-04-13 9:46 ` Peter Zijlstra
2018-04-13 11:08 ` Patrick Bellasi [this message]
2018-04-13 11:19 ` Peter Zijlstra
2018-04-09 16:56 ` [PATCH 2/7] sched/core: uclamp: map TASK clamp values into CPU clamp groups Patrick Bellasi
2018-04-09 16:56 ` [PATCH 3/7] sched/core: uclamp: extend sched_setattr to support utilization clamping Patrick Bellasi
2018-04-09 16:56 ` [PATCH 4/7] sched/core: uclamp: add utilization clamping to the CPU controller Patrick Bellasi
2018-04-09 22:24 ` Tejun Heo
2018-04-10 17:16 ` Patrick Bellasi
2018-04-10 20:05 ` Tejun Heo
2018-04-21 21:08 ` Joel Fernandes
2018-04-26 18:58 ` Tejun Heo
2018-04-09 16:56 ` [PATCH 5/7] sched/core: uclamp: use TG clamps to restrict TASK clamps Patrick Bellasi
2018-04-09 16:56 ` [PATCH 6/7] sched/cpufreq: uclamp: add utilization clamping for FAIR tasks Patrick Bellasi
2018-04-09 16:56 ` [PATCH 7/7] sched/cpufreq: uclamp: add utilization clamping for RT tasks Patrick Bellasi
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