Re: [PATCH v2 1/2] x86,sched: Add support for frequency invariance

From: Peter Zijlstra <peterz@infradead.org>
To: Giovanni Gherdovich <ggherdovich@suse.cz>
Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@suse.de>,
	Len Brown <lenb@kernel.org>,
	"Rafael J . Wysocki" <rjw@rjwysocki.net>,
	x86@kernel.org, linux-pm@vger.kernel.org,
	linux-kernel@vger.kernel.org,
	Mel Gorman <mgorman@techsingularity.net>,
	Matt Fleming <matt@codeblueprint.co.uk>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Juri Lelli <juri.lelli@redhat.com>, Paul Turner <pjt@google.com>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	Quentin Perret <qperret@qperret.net>,
	Dietmar Eggemann <dietmar.eggemann@arm.com>,
	Doug Smythies <dsmythies@telus.net>
Subject: Re: [PATCH v2 1/2] x86,sched: Add support for frequency invariance
Date: Wed, 2 Oct 2019 20:27:55 +0200	[thread overview]
Message-ID: <20191002182754.GD4643@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <20191002122926.385-2-ggherdovich@suse.cz>

On Wed, Oct 02, 2019 at 02:29:25PM +0200, Giovanni Gherdovich wrote:
> +void x86_arch_scale_freq_tick_enable(void)
> +{
> +	tick_disable = false;
> +}
> +
> +static void reset_scale_freq(void *arg)
> +{
> +	this_cpu_write(arch_cpu_freq, SCHED_CAPACITY_SCALE);
> +}
> +
> +void x86_arch_scale_freq_tick_disable(void)
> +{
> +	on_each_cpu(reset_scale_freq, NULL, 1);
> +	tick_disable = true;

I'm thikning this ought to be the other way around, otherwise we can get
a tick loosing the 1024 we just wrote in arch_cpu_freq.

> +}

You've lost the prev_{a,m}perf update, so the first tick after enable
will see 'funny' values.