linux-kernel - Re: [PATCH v1 0/4] cpufreq: Allow drivers to receive more information from the governor

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Message-ID: <20201218153231.GB2414@hirez.programming.kicks-ass.net>
Date:   Fri, 18 Dec 2020 16:32:31 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Doug Smythies <dsmythies@...us.net>
Cc:     "'Rafael J. Wysocki'" <rafael@...nel.org>,
        'Giovanni Gherdovich' <ggherdovich@...e.com>,
        "'Rafael J. Wysocki'" <rjw@...ysocki.net>,
        'Linux PM' <linux-pm@...r.kernel.org>,
        'LKML' <linux-kernel@...r.kernel.org>,
        'Viresh Kumar' <viresh.kumar@...aro.org>,
        'Srinivas Pandruvada' <srinivas.pandruvada@...ux.intel.com>,
        efault@....de, Mel Gorman <mgorman@...e.de>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Juri Lelli <juri.lelli@...il.com>
Subject: Re: [PATCH v1 0/4] cpufreq: Allow drivers to receive more
 information from the governor

On Tue, Dec 08, 2020 at 11:14:36AM -0800, Doug Smythies wrote:
> At least on my system, it is most evident for some of the pipe type tests,
> where the schedutil governor has never really known what to do. This patch
> set seems to add enough of a downward bias that this version of the schedutil
> governor now behaves much like the other versions

Yeah, pipe relies on task-task interaction, where one task waits on
another, and by boosting the producer the consumer can start earlier and
we get more cycles done etc.. Rather similar to IO-wait, where by
boosting the producer we gain throughput.

schedutil doesn't track anything useful here, but it is a semi common
pattern and it would be really good if we could somehow fix this.

We obviously have access to the task A wakes task B information, but I'm
not sure what to do with it, we're tried some things like this in the
past (although for slightly different reasons) and they've always ended
up being a mess :/