Re: [PATCH v6 04/11] cpufreq/schedutil: use rt utilization tracking

From: Peter Zijlstra <peterz@infradead.org>
To: Quentin Perret <quentin.perret@arm.com>
Cc: Vincent Guittot <vincent.guittot@linaro.org>,
	mingo@kernel.org, linux-kernel@vger.kernel.org,
	rjw@rjwysocki.net, juri.lelli@redhat.com,
	dietmar.eggemann@arm.com, Morten.Rasmussen@arm.com,
	viresh.kumar@linaro.org, valentin.schneider@arm.com,
	patrick.bellasi@arm.com, joel@joelfernandes.org,
	daniel.lezcano@linaro.org, Ingo Molnar <mingo@redhat.com>
Subject: Re: [PATCH v6 04/11] cpufreq/schedutil: use rt utilization tracking
Date: Fri, 22 Jun 2018 15:29:53 +0200	[thread overview]
Message-ID: <20180622132953.GM2494@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20180622125433.GA26461@e108498-lin.cambridge.arm.com>

On Fri, Jun 22, 2018 at 01:54:34PM +0100, Quentin Perret wrote:
> On Friday 22 Jun 2018 at 13:37:13 (+0200), Peter Zijlstra wrote:
> > That is true.. So we could limit the scaling to the case where there is
> > no idle time, something like:
> > 
> > 	util = sg_cpu->util_cfs;
> > 
> > 	cap_cfs = (1024 - (sg_cpu->util_rt + ...));
> > 	if (util == cap_cfs)
> > 		util = sg_cpu->max;
> > 
> > That specifically handles the '0% idle -> 100% freq' case, but I don't
> > realy like edge behaviour like that. If for some reason it all doesn't
> > quite align you're left with bits.
> > 
> > And the linear scaling is the next simplest thing that avoids the hard
> > boundary case.
> 
> Right, so maybe we'll get something smoother by just summing the signals
> as Vincent is proposing ? 

Sure, but see my previous mail just now, that has the problem of
u_{rt,dl} distoting f_{rt,dl} even when there is no u_cfs.