linux-kernel - Re: [PATCH] cpuidle: poll_state: Avoid invoking local

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Message-ID: <1522188032.6308.69.camel@surriel.com>
Date:   Tue, 27 Mar 2018 18:00:32 -0400
From:   Rik van Riel <riel@...riel.com>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM <linux-pm@...r.kernel.org>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Frederic Weisbecker <fweisbec@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Thomas Ilsche <thomas.ilsche@...dresden.de>,
        Doug Smythies <dsmythies@...us.net>,
        Aubrey Li <aubrey.li@...ux.intel.com>,
        Mike Galbraith <mgalbraith@...e.de>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cpuidle: poll_state: Avoid invoking local_clock() too
 often

On Tue, 2018-03-27 at 23:58 +0200, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> Rik reports that he sees an increase in CPU use in one benchmark
> due to commit 612f1a22f067 "cpuidle: poll_state: Add time limit to
> poll_idle()" that caused poll_idle() to call local_clock() in every
> iteration of the loop.  Utilization increase generally means more
> non-idle time with respect to total CPU time (on the average) which
> implies reduced CPU frequency.
> 
> Doug reports that limiting the rate of local_clock() invocations
> in there causes much less power to be drawn during a CPU-intensive
> parallel workload (with idle states 1 and 2 disabled to enforce more
> state 0 residency).
> 
> These two reports together suggest that executing local_clock() on
> multiple CPUs in parallel at a high rate may cause chips to get hot
> and trigger thermal/power limits on them to kick in, so reduce the
> rate of local_clock() invocations in poll_idle() to avoid that issue.
> 
> Fixes: 612f1a22f067 "cpuidle: poll_state: Add time limit to
> poll_idle()"
> Reported-by: Rik van Riel <riel@...riel.com>
> Reported-by: Doug Smythies <dsmythies@...us.net>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

Thanks Rafael!

Tested-by: Rik van Riel <riel@...riel.com>
Reviewed-by: Rik van Riel <riel@...riel.com>

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