linux-kernel - Re: [PATCH V2 3/3] cpufreq: CPPC: Add support for frequency invariance

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Message-ID: <YMs+hOKafJMu7Sfu@hirez.programming.kicks-ass.net>
Date:   Thu, 17 Jun 2021 14:22:28 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Ionela Voinescu <ionela.voinescu@....com>,
        Rafael Wysocki <rjw@...ysocki.net>,
        Sudeep Holla <sudeep.holla@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        linux-pm@...r.kernel.org, Qian Cai <quic_qiancai@...cinc.com>,
        linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 3/3] cpufreq: CPPC: Add support for frequency
 invariance

On Thu, Jun 17, 2021 at 04:49:36PM +0530, Viresh Kumar wrote:
> Peter: Can you help here on this ? Lemme try to explain a bit here:
> 
> We are starting an irq-work (in cppc cpufreq driver) from
> scheduler_tick()->arch_scale_freq_tick(). What will happen if the driver doesn't
> take care of CPU hotplug explicitly and make sure this work isn't queued again
> from the next tick.
> 
> Is it important for user to make sure it gets rid of the irq-work during hotplug
> here ?

irq-work is flushed on hotplug, see smpcfd_dying_cpu().