linux-kernel - Re: [RFT][Update][PATCH 2/2] cpufreq: intel_pstate: Update max CPU frequency on global turbo changes

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Message-ID: <20190305114406.GV32494@hirez.programming.kicks-ass.net>
Date:   Tue, 5 Mar 2019 12:44:06 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Quentin Perret <quentin.perret@....com>,
        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>,
        Chen Yu <yu.c.chen@...el.com>,
        Gabriele Mazzotta <gabriele.mzt@...il.com>
Subject: Re: [RFT][Update][PATCH 2/2] cpufreq: intel_pstate: Update max CPU
 frequency on global turbo changes

On Tue, Mar 05, 2019 at 11:58:37AM +0100, Rafael J. Wysocki wrote:
> So after the Peter's patch "sched/cpufreq: Fix 32bit math overflow"
> I will need to recompute sg_cpu->min in sugov_limits().

So there's still an open question; do we want that ->min thing to depend
on available frequencies _at_all_ ?

I'm thinking it might be a good thing to have the iowait boost curve be
independent of all that.

Like said; if we set it at 128 (static), it takes 9 consequtive wake-ups
for it to reach 1024 (max). While now the curve depends on how wide the
gap is between min_freq and max_freq. And it seems weird to have this
behaviour depend on that. To me at least.

Now, I don't know if 128/9 is the right curve, it is just a random
number I pulled out of a hat. But it seems to make more sense than
depending on frequencies.