linux-kernel - Re: [PATCH v2] cpufreq: schedutil: Trace frequency only if it has changed

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Date:   Thu, 23 Mar 2017 10:02:13 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     Linux PM <linux-pm@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Patrick Bellasi <patrick.bellasi@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [PATCH v2] cpufreq: schedutil: Trace frequency only if it has
 changed

On 22-03-17, 18:32, Rafael J. Wysocki wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> 
> sugov_update_commit() calls trace_cpu_frequency() to record the
> current CPU frequency if it has not changed in the fast switch case
> to prevent utilities from getting confused (they may report that the
> CPU is idle if the frequency has not been recorded for too long, for
> example).
> 
> However, that may cause the tracepoint to be triggered quite often
> for no real reason (if the frequency doesn't change, we will not
> modify the last update time stamp and governor computations may
> run again shortly when that happens), so don't do that (arguably, it
> is done to work around a utilities bug anyway).
> 
> That allows code duplication in sugov_update_commit() to be reduced
> somewhat too.
> 
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> ---
> 
> -> v2:
> Drop the trace_cpu_frequency() call in the sg_policy->next_freq == next_freq case.
> 
> ---
>  kernel/sched/cpufreq_schedutil.c |   16 +++++++---------
>  1 file changed, 7 insertions(+), 9 deletions(-)

Acked-by: Viresh Kumar <viresh.kumar@...aro.org>

-- 
viresh