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

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Message-ID: <alpine.DEB.2.21.1903211645100.1784@nanos.tec.linutronix.de>
Date:   Thu, 21 Mar 2019 16:49:37 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Viresh Kumar <viresh.kumar@...aro.org>
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 Wed, 20 Mar 2019, Viresh Kumar wrote:

> Currently we call these notifiers once for each CPU of the policy->cpus

Nitpick: We call nothing. The notifiers are called ....

> cpumask. It would be more optimal if the notifier can be called only
> once and all the relevant information be provided to it. Out of the 23
> 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 ....

Thanks,

	tglx