linux-kernel - Re: [PATCH RFC v4] cpufreq: schedutil: Make iowait boost more energy efficient

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Message-ID: <20170712132824.mnoevjtm6wd6yh2c@hirez.programming.kicks-ass.net>
Date:   Wed, 12 Jul 2017 15:28:24 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Joel Fernandes <joelaf@...gle.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Juri Lelli <juri.lelli@....com>,
        Andres Oportus <andresoportus@...gle.com>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Len Brown <lenb@...nel.org>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH RFC v4] cpufreq: schedutil: Make iowait boost more energy
 efficient

On Wed, Jul 12, 2017 at 03:16:23PM +0530, Viresh Kumar wrote:

> No, I wasn't clear enough. Sorry about that. Lemme try again:
> 
> Suppose min freq is 500 MHz and Max is 2 GHz. The iowait-boost is
> set to 1 GHz right now (because of previous events with IOWAIT flag
> set), and sugov_set_iowait_boost() gets called again with IOWAIT flag,
> we boost the iowait-boost value to 2 GHz. We are in the rate_limit_us
> window right now, we return without changing the frequency.
> 
> If the next call into the schedutil governor happens due to normal
> util-update, flags will be passed as 0. With the current patch, we
> will bring iowait-boost back to 1 GHz (before updating the real
> frequency to 2 GHz) as the prev-iowait-boost boolean would be set.
> 
> And even if the task is periodically getting queued after IOWAIT,
> actual boosting may not happen at all in some cases.

Hmm, so you're worried about that ratelimit stuff? Shouldn't we fix that
independently -- IIRC Rafael proposed a max-filter over the window.