linux-kernel - Re: [PATCH] cpufreq: schedutil: Don't use the limits

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Date:   Tue, 9 Feb 2021 16:41:23 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Yue Hu <zbestahu@...il.com>
Cc:     rjw@...ysocki.net, rafael.j.wysocki@...el.com, mingo@...hat.com,
        peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, linux-pm@...r.kernel.org,
        linux-kernel@...r.kernel.org, huyue2@...ong.com, zbestahu@....com,
        zhangwen@...ong.com
Subject: Re: [PATCH] cpufreq: schedutil: Don't use the limits_changed flag
 any more

On 08-02-21, 11:07, Yue Hu wrote:
> From: Yue Hu <huyue2@...ong.com>
> 
> The limits_changed flag was introduced by commit 600f5badb78c
> ("cpufreq: schedutil: Don't skip freq update when limits change") due
> to race condition where need_freq_update is cleared in get_next_freq()
> which causes reducing the CPU frequency is ineffective while busy.
> 
> But now, the race condition above is gone because get_next_freq()
> doesn't clear the flag any more after commit 23a881852f3e ("cpufreq:
> schedutil: Don't skip freq update if need_freq_update is set").
> 
> Moreover, need_freq_update currently will be set to true only in
> sugov_should_update_freq() if CPUFREQ_NEED_UPDATE_LIMITS is not set
> for the driver. However, limits may have changed at any time. And
> subsequent frequence update is depending on need_freq_update. So, we
> may skip this update.
> 
> Hence, let's remove it to avoid above issue and make code more simple.
> 
> Signed-off-by: Yue Hu <huyue2@...ong.com>
> ---
>  kernel/sched/cpufreq_schedutil.c | 11 +++--------
>  1 file changed, 3 insertions(+), 8 deletions(-)

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

-- 
viresh