linux-kernel - Re: [tip: sched/core] x86, sched: Add support for frequency invariance

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Message-ID: <jhjimil25l3.mognet@arm.com>
Date:   Mon, 30 Mar 2020 17:03:04 +0100
From:   Valentin Schneider <valentin.schneider@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Chris Wilson <chris@...is-wilson.co.uk>,
        linux-kernel@...r.kernel.org, linux-tip-commits@...r.kernel.org,
        tip-bot2 for Giovanni Gherdovich <tip-bot2@...utronix.de>,
        Giovanni Gherdovich <ggherdovich@...e.cz>,
        Ingo Molnar <mingo@...nel.org>,
        Doug Smythies <dsmythies@...us.net>,
        "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
        x86 <x86@...nel.org>
Subject: Re: [tip: sched/core] x86, sched: Add support for frequency invariance


On Mon, Mar 30 2020, Peter Zijlstra wrote:
> +static void init_freq_invariance(bool secondary)
>  {
>  	bool ret = false;
>  
> -	if (smp_processor_id() != 0 || !boot_cpu_has(X86_FEATURE_APERFMPERF))
> +	if (!boot_cpu_has(X86_FEATURE_APERFMPERF))
>  		return;
>  
> +	if (secondary) {
> +		if (static_branch_likely(&arch_scale_freq_key)) {
> +			init_counter_refs(NULL);
> +		}
> +		return;
> +	}
> +

Oh doh, that's an "enable once and for all" thing. That makes much more
sense; sorry for the noise.