Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Fri, 18 Oct 2019 10:11:53 +0200
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
Message-ID: <20191018081153.GE2328@hirez.programming.kicks-ass.net>
References: <20191011134500.235736-1-douglas.raillard@arm.com>
 <20191014145315.GZ2311@hirez.programming.kicks-ass.net>
 <a1ce67d7-62c3-b78b-1d87-23ef4dbc2274@arm.com>
 <20191017095015.GI2311@hirez.programming.kicks-ass.net>
 <20191017111116.GA27006@google.com>
 <20191017141107.GJ2311@hirez.programming.kicks-ass.net>
 <2cbde0fe-c10c-0ebb-32ef-2d522986bc89@arm.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <2cbde0fe-c10c-0ebb-32ef-2d522986bc89@arm.com>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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.