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

From: Thomas Gleixner <tglx@linutronix.de>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: "Rafael Wysocki" <rjw@rjwysocki.net>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"Russell King" <linux@armlinux.org.uk>,
	"David S. Miller" <davem@davemloft.net>,
	"Ingo Molnar" <mingo@redhat.com>,
	"Borislav Petkov" <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	x86@kernel.org, "Paolo Bonzini" <pbonzini@redhat.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>,
	linux-pm@vger.kernel.org,
	"Vincent Guittot" <vincent.guittot@linaro.org>,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, sparclinux@vger.kernel.org,
	kvm@vger.kernel.org
Subject: Re: [PATCH V3] cpufreq: Call transition notifier only once for each policy
Date: Thu, 21 Mar 2019 16:49:37 +0100 (CET)	[thread overview]
Message-ID: <alpine.DEB.2.21.1903211645100.1784@nanos.tec.linutronix.de> (raw)
In-Reply-To: <1eb27e3bbcbb2c67e6eadc0893c9b41e5d76894b.1553057341.git.viresh.kumar@linaro.org>

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