linux-kernel - Re: [PATCH] cpufreq: schedutil: add up/down frequency transition rate limits

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Date:   Mon, 21 Nov 2016 12:14:32 +0000
From:   Juri Lelli <Juri.Lelli@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Viresh Kumar <viresh.kumar@...aro.org>,
        Rafael Wysocki <rjw@...ysocki.net>,
        Ingo Molnar <mingo@...hat.com>, linaro-kernel@...ts.linaro.org,
        linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Robin Randhawa <robin.randhawa@....com>,
        Steve Muckle <smuckle.linux@...il.com>, tkjos@...gle.com,
        Morten Rasmussen <morten.rasmussen@....com>
Subject: Re: [PATCH] cpufreq: schedutil: add up/down frequency transition
 rate limits

On 21/11/16 11:19, Peter Zijlstra wrote:
> On Mon, Nov 21, 2016 at 03:38:05PM +0530, Viresh Kumar wrote:
> > On 17-11-16, 10:48, Viresh Kumar wrote:

[...]

> > 
> > (Background story for others from my discussion with Rafael on IRC: Rafael
> > proposed that instead of this patch we can add down_rate_limit_delta_us (>0 =)
> > which can be added to rate_limit_us (rate limit while increasing freq) to find
> > the rate limit to be used in the downward direction. And I raised the point
> > that it looks much neater to have separate up and down rate_limit_us. I also
> > said that people may have a valid case where they want to keep down_rate_limit
> > lower than up_rate_limit and Rafael wasn't fully sure of any such cases).
> > 
> 
> Urgh...
> 
> 
> So no tunables and rate limits here at all please.
> 
> During LPC we discussed the rampup and decay issues and decided that we
> should very much first address them by playing with the PELT stuff.
> Morton was going to play with capping the decay on the util signal. This
> should greatly improve the ramp-up scenario and cure some other wobbles.
> 
> The decay can be set by changing the over-all pelt decay, if so desired.
> 

Do you mean we might want to change the decay (make it different from
ramp-up) once for all, or maybe we make it tunable so that we can
address different power/perf requirements?

> Also, there was the idea of; once the above ideas have all been
> explored; tying the freq ram rate to the power curve.
> 

Yep. That's an interesting one to look at, but it might require some
time.

> So NAK on everything tunable here.