linux-kernel - Re: [PATCH V3] cpufreq: Call transition notifier only once for each policy

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Date:   Fri, 22 Mar 2019 11:57:44 +0530
From:   Viresh Kumar <viresh.kumar@...aro.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Rafael Wysocki <rjw@...ysocki.net>,
        Peter Zijlstra <peterz@...radead.org>,
        Russell King <linux@...linux.org.uk>,
        "David S. Miller" <davem@...emloft.net>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        linux-pm@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        sparclinux@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH V3] cpufreq: Call transition notifier only once for each
 policy

On 21-03-19, 16:49, Thomas Gleixner wrote:
> On Wed, 20 Mar 2019, Viresh Kumar wrote:
> >
> > diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c
> > index 3fae23834069..b2fe665878f7 100644
> > --- a/arch/x86/kernel/tsc.c
> > +++ b/arch/x86/kernel/tsc.c
> > @@ -958,10 +958,15 @@ static int time_cpufreq_notifier(struct notifier_block *nb, unsigned long val,
> >  	struct cpufreq_freqs *freq = data;
> >  	unsigned long *lpj;
> >  
> > +	if (WARN_ON_ONCE(cpumask_weight(freq->policy->related_cpus) != 1)) {
> > +		mark_tsc_unstable("cpufreq changes: related CPUs affected");
> > +		return 0;
> > +	}
> 
> You might add a check which ensures that policy->cpu == smp_processor_id()
> because if this is not the case ....

How about something like this ?

	if (WARN_ON_ONCE(cpumask_weight(freq->policy->related_cpus) != 1 ||
                         freq->policy->cpu != smp_processor_id())) {
		mark_tsc_unstable("cpufreq changes: related CPUs affected");
		return 0;
	}


Thanks for your feedback.

-- 
viresh