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Date:   Fri, 19 Feb 2021 19:45:09 +0800
From:   Yue Hu <zbestahu@gmail.com>
To:     Viresh Kumar <viresh.kumar@linaro.org>
Cc:     rjw@rjwysocki.net, mingo@redhat.com, peterz@infradead.org,
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        linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org,
        huyue2@yulong.com, zbestahu@163.com
Subject: Re: [PATCH] cpufreq: schedutil: Don't consider freq reduction to
 busy CPU if need_freq_update is set
Message-ID: <20210219194509.00005884.zbestahu@gmail.com>
In-Reply-To: <20210219093551.bykqhjk6xvs4kszi@vireshk-i7>
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On Fri, 19 Feb 2021 15:05:51 +0530
Viresh Kumar <viresh.kumar@linaro.org> wrote:

> On 19-02-21, 16:20, Yue Hu wrote:
> > However, we will skip the update if need_freq_update is not set.  
> 
> Not really, we will update freq periodically nevertheless, around
> every 10ms or something..
> 
> > And do the update if need_freq_update is set.  
> 
> Yeah, that breaks the periodic cycle to attend to some urgent request.
> 
> > Note that there are unnecessary fast switch check and spin
> > lock/unlock operations in freq skip path.  
> 
> Maybe, I am not sure. We are all up for optimizations if there are
> any.

We will set next_f to next_freq(previous freq) if next_f is
reduced for busy CPU. Then the next sugov_update_next_freq() will check
if next_freq matches next_f if need_freq_update is not set.
Obviously, we will do nothing for the case. And The related check to
fast_switch_enabled and raw_spin_{lock,unlock} operations are
unnecessary.

> 
> > If we consider unnecessary behaviors above, then we should return
> > right away rather than continue to execute following code.  
> 
> As I said earlier, we may end up updating the frequency even if
> need_freq_update is unset.
>