linux-kernel - Re: [PATCH][v2] sched: cpufreq: Fix long idle judgement logic in load calculation

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Message-ID: <20180608040413.2pjfr6by3me5qymk@vireshk-i7>
Date:   Fri, 8 Jun 2018 09:34:13 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Chen Yu <yu.c.chen@...el.com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        linux-kernel@...r.kernel.org,
        Artem S Tashkinov <t.artem@...lcity.com>,
        linux-pm@...r.kernel.org
Subject: Re: [PATCH][v2] sched: cpufreq: Fix long idle judgement logic in
 load calculation

On 08-06-18, 09:07, Chen Yu wrote:
> According to current code implementation, detecting the long
> idle period is done by checking if the interval between two
> adjacent utilization update handers is long enough. Although
> this mechanism can detect if the idle period is long enough
> (no utilization hooks invoked during idle period), it might
> not contain a corner case: if the task has occupied the cpu
> for too long which causes no context switch during that
> period, then no utilization handler will be launched until this
> high prio task is switched out. As a result, the idle_periods
> field might be calculated incorrectly because it regards the
> 100% load as 0% and makes the conservative governor who uses
> this field confusing.
> 
> Change the judgement to compare the idle_time with sampling_rate
> directly.
> 
> Reported-by: Artem S. Tashkinov <t.artem@...lcity.com>
> Cc: Artem S Tashkinov <t.artem@...lcity.com>
> Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> Cc: Viresh Kumar <viresh.kumar@...aro.org>
> Cc: linux-pm@...r.kernel.org
> Signed-off-by: Chen Yu <yu.c.chen@...el.com>
> ---
> v2: Per Viresh's suggestion, ignore idle_time longer than 30mins and
>     simplify the code.
> ---
>  drivers/cpufreq/cpufreq_governor.c | 12 +++++-------
>  1 file changed, 5 insertions(+), 7 deletions(-)

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

-- 
viresh