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Date: Mon, 15 Feb 2021 12:00:08 +0530 From: Viresh Kumar <viresh.kumar@...aro.org> To: Yue Hu <zbestahu@....com> Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Yue Hu <zbestahu@...il.com>, "Rafael J. Wysocki" <rjw@...ysocki.net>, Rafael Wysocki <rafael.j.wysocki@...el.com>, Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>, Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot <vincent.guittot@...aro.org>, Dietmar Eggemann <dietmar.eggemann@....com>, Steven Rostedt <rostedt@...dmis.org>, Benjamin Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>, Daniel Bristot de Oliveira <bristot@...hat.com>, Linux PM <linux-pm@...r.kernel.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org>, Yue Hu <huyue2@...ong.com>, zhangwen@...ong.com Subject: Re: [PATCH] cpufreq: schedutil: Don't use the limits_changed flag any more On 14-02-21, 11:44, Yue Hu wrote: > On Fri, 12 Feb 2021 17:14:03 +0100 > "Rafael J. Wysocki" <rafael@...nel.org> wrote: > > This may be running in parallel with sugov_update_next_freq() on a > > different CPU, so the latter may clear need_freq_update right after it > > has been set here unless I'm overlooking something. > > Whether this logic is also happening for limits_changed in > sugo_should_update_freq() or not? It is but it shouldn't have any side effects as we calculate the next frequency after cleaning the limits_changed flag. Your patch would have been fine, but it is not anymore because of commit 23a881852f3e ("cpufreq: schedutil: Don't skip freq update if need_freq_update is set"). It made a considerable change after which your patch adds a bug. With 23a881852f3e, need_freq_update is updated/cleared after the next frequency is calculated, while earlier it was cleared before it. And so even with the race condition taking place, there were no issues. -- viresh
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