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From: Peter Zijlstra <peterz@infradead.org>
To: Dietmar Eggemann <dietmar.eggemann@arm.com>
Cc: Quentin Perret <qperret@google.com>,
	Douglas Raillard <douglas.raillard@arm.com>,
	linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
	mingo@redhat.com, rjw@rjwysocki.net, viresh.kumar@linaro.org,
	juri.lelli@redhat.com, vincent.guittot@linaro.org,
	qperret@qperret.net, patrick.bellasi@matbug.net,
	dh.han@samsung.com
Subject: Re: [RFC PATCH v3 0/6] sched/cpufreq: Make schedutil energy aware
Date: Fri, 18 Oct 2019 10:11:53 +0200
Message-ID: <20191018081153.GE2328@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <2cbde0fe-c10c-0ebb-32ef-2d522986bc89@arm.com>

On Fri, Oct 18, 2019 at 09:44:44AM +0200, Dietmar Eggemann wrote:
> On 17/10/2019 16:11, Peter Zijlstra wrote:
> > On Thu, Oct 17, 2019 at 12:11:16PM +0100, Quentin Perret wrote:
> 
> [...]
> 
> > It only boosts when 'rq->cfs.avg.util' increases while
> > 'rq->cfs.avg.util_est.enqueued' remains unchanged (and util > util_est
> > obv).
> > 
> > This condition can be true for select_task_rq_fair(), because that is
> > ran before we do enqueue_task_fair() (for obvious raisins).
> > 
> >>> I'm still thinking about the exact means you're using to raise C; that
> >>> is, the 'util - util_est' as cost_margin. It hurts my brain still.
> >>
> >> +1 ...
> > 
> > cost_i = capacity_i / power_i ; for the i-th OPP
> 
> I get confused by this definition. efficiency=capacity/power but the
> cs->cost value used in em_pd_get_higher_freq() is defined as
> 
> cs_cost = cs->power * cpu_max_freq / cs->freq [energy_model.h]

	cost_i = power_i * f_max / f_i

	cost(x) = cost_j * (1 + x) ; f_j >= min_freq

	cost_k <= cost(x)

	P = C*V^2*f, V ~ f -> P ~ f^3

	cost_i ~ f_i^3 * f_max / f_i
	       = f_i^2 * f_max

	cost(x) = (1 + x) * f_j^2 * f_max

	cost_k = cost(x)

	f_k^2 * f_max = (1 + x) * f_j^2 * f_max

	f_k = sqrt(1 + x) * f_j

Which does indeed make more sense... However, I still struggle with
using our 'x = util - util_est' as input for an OPP specific increase.


  parent reply index

Thread overview: 35+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-11 13:44 Douglas RAILLARD
2019-10-11 13:44 ` [RFC PATCH v3 1/6] PM: Introduce em_pd_get_higher_freq() Douglas RAILLARD
2019-10-17  8:57   ` Dietmar Eggemann
2019-10-17  9:58   ` Dietmar Eggemann
2019-10-17 11:09     ` Douglas Raillard
2019-10-11 13:44 ` [RFC PATCH v3 2/6] sched/cpufreq: Attach perf domain to sugov policy Douglas RAILLARD
2019-10-17  8:57   ` Dietmar Eggemann
2019-10-17 10:22     ` Douglas Raillard
2019-10-11 13:44 ` [RFC PATCH v3 3/6] sched/cpufreq: Hook em_pd_get_higher_power() into get_next_freq() Douglas RAILLARD
2019-10-11 13:44 ` [RFC PATCH v3 4/6] sched/cpufreq: Introduce sugov_cpu_ramp_boost Douglas RAILLARD
2019-10-14 14:33   ` Peter Zijlstra
2019-10-14 15:32     ` Douglas Raillard
2019-10-17  8:57   ` Dietmar Eggemann
2019-10-17 11:19     ` Douglas Raillard
2019-10-11 13:44 ` [RFC PATCH v3 5/6] sched/cpufreq: Boost schedutil frequency ramp up Douglas RAILLARD
2019-10-17  9:21   ` Dietmar Eggemann
2019-10-11 13:45 ` [RFC PATCH v3 6/6] sched/cpufreq: Add schedutil_em_tp tracepoint Douglas RAILLARD
2019-10-14 14:53 ` [RFC PATCH v3 0/6] sched/cpufreq: Make schedutil energy aware Peter Zijlstra
2019-10-14 15:50   ` Douglas Raillard
2019-10-17  9:50     ` Peter Zijlstra
2019-10-17 11:11       ` Quentin Perret
2019-10-17 14:11         ` Peter Zijlstra
2019-10-18  7:44           ` Dietmar Eggemann
2019-10-18  7:59             ` Peter Zijlstra
2019-10-18 17:24               ` Douglas Raillard
2019-10-18  8:11             ` Peter Zijlstra [this message]
2019-10-17 14:23       ` Douglas Raillard
2019-10-17 14:53         ` Peter Zijlstra
2019-10-17 19:07         ` Peter Zijlstra
2019-10-18 11:46           ` Douglas Raillard
2019-10-18 12:07             ` Peter Zijlstra
2019-10-18 14:44               ` Douglas Raillard
2019-10-18 15:15                 ` Vincent Guittot
2019-10-18 16:03                   ` Douglas Raillard
2019-10-18 15:20                 ` Vincent Guittot

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