linux-kernel - Re: [PATCH v1 2/4] cpufreq: schedutil: Adjust utilization instead of frequency

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Message-ID: <20201214110717.boz634eih2ymjtju@vireshk-i7>
Date:   Mon, 14 Dec 2020 16:37:17 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Doug Smythies <dsmythies@...us.net>,
        Giovanni Gherdovich <ggherdovich@...e.com>
Subject: Re: [PATCH v1 2/4] cpufreq: schedutil: Adjust utilization instead of
 frequency

On 09-12-20, 16:32, Rafael J. Wysocki wrote:
> So I have misunderstood your example.
> 
> In the non-invariant case (which is or shortly will be relevant for
> everybody interested) cpuinfo.max_freq goes into the calculation
> instead of the current frequency and the mapping between util and freq
> is linear.  In the freq-dependent case it is not linear, of course.
> 
> So I guess the concern is that this changes the behavior in the
> freq-dependent case which may not be desirable.

Right and we end up increasing the frequency here..

> Fair enough, but I'm not sure if that is enough of a reason to avoid
> sharing the code between the "perf" and "freq" paths.

Sure, I am not against sharing the code path, but all we need is
something like this here:

     if (sugov_cpu_is_busy(sg_cpu) && sg_cpu->util < prev_util)
             sg_cpu->util = prev_util;
     else
             next_f = get_next_freq(sg_policy, sg_cpu->util, sg_cpu->max);

i.e. we don't need to call get_next_freq() in this case at all.

-- 
viresh