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From: Peter Zijlstra <peterz@infradead.org>
To: Giovanni Gherdovich <ggherdovich@suse.cz>
Cc: Quentin Perret <qperret@qperret.net>,
	srinivas.pandruvada@linux.intel.com, tglx@linutronix.de,
	mingo@redhat.com, bp@suse.de, lenb@kernel.org, rjw@rjwysocki.net,
	x86@kernel.org, linux-pm@vger.kernel.org,
	linux-kernel@vger.kernel.org, mgorman@techsingularity.net,
	matt@codeblueprint.co.uk, viresh.kumar@linaro.org,
	juri.lelli@redhat.com, pjt@google.com,
	vincent.guittot@linaro.org, dietmar.eggemann@arm.com
Subject: Re: [PATCH 1/2] x86,sched: Add support for frequency invariance
Date: Wed, 2 Oct 2019 20:45:00 +0200	[thread overview]
Message-ID: <20191002184500.GF4643@worktop.programming.kicks-ass.net> (raw)
In-Reply-To: <1570019274.22393.2.camel@suse.cz>

On Wed, Oct 02, 2019 at 02:27:54PM +0200, Giovanni Gherdovich wrote:
> On Tue, 2019-09-24 at 18:00 +0200, Peter Zijlstra wrote:
> > On Tue, Sep 24, 2019 at 04:03:32PM +0200, Peter Zijlstra wrote:
> > 
> > > > I'll check what's the cost of static_cpu_has() and if it's non-negligible I'll
> > > > do what you suggest (x86-specific version of arch_scale_freq_invariant().
> > > 
> > > static_cpu_has() is an alternative and ends up being a static branch
> > > (similar to static_key) once the alternative patching runs.
> > 
> > That said; I think you want a static key anyway, because if we can't
> > tell the max_freq we don't want to use the invariant stuff.
> > 
> > Something a little like so on top perhaps.
> > 
> > Also, the below fixes that silly tick_disable stuff.
> 
> Thanks for this patch, I'll add this change in v2.
> 
> Can you elaborate on what you don't like in the tick_disable mechanism?

Mostly because I dislike intel_pstate active mode a lot, but also
because it makes PELT behave differently between pstate and !pstate.

> > +static void init_scale_freq(void *arg)
> >  {
> >  	u64 aperf, mperf;
> >  
> > +	rdmsrl(MSR_IA32_APERF, aperf);
> > +	rdmsrl(MSR_IA32_MPERF, mperf);
> > +
> > +	this_cpu_write(arch_prev_aperf, aperf);
> > +	this_cpu_write(arch_prev_mperf, mperf);
> > +}
> > +

> > @@ -1940,5 +1949,6 @@ void x86_arch_scale_freq_tick_enable(voi
> >  
> >  void x86_arch_scale_freq_tick_disable(void)
> >  {
> > +	on_each_cpu(init_scale_freq, NULL, 1);
> >  	tick_disable = true;
> 
> I don't see why the call init_scale_freq() here is needed; why would I care of
> what's in arch_prev_[am]perf at this point. arch_scale_freq_tick() will see
> that tick_disable == true and exit early before reading arch_prev_[am]perf.

You're right, we should reset the prev values on enable. Otherwise the
first tick after enable will see 'weird' values.

  reply	other threads:[~2019-10-02 18:45 UTC|newest]

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-09-09  2:42 [PATCH 0/2] Add support for frequency invariance for (some) x86 Giovanni Gherdovich
2019-09-09  2:42 ` [PATCH 1/2] x86,sched: Add support for frequency invariance Giovanni Gherdovich
2019-09-11 15:28   ` Doug Smythies
2019-09-13 20:58     ` Doug Smythies
2019-09-17 14:25       ` Giovanni Gherdovich
2019-09-19 14:42         ` Doug Smythies
2019-09-24  8:06           ` Mel Gorman
2019-09-24 17:52             ` Doug Smythies
2019-09-13 22:52   ` Srinivas Pandruvada
2019-09-17 14:27     ` Giovanni Gherdovich
2019-09-17 15:55       ` Vincent Guittot
2019-09-19 23:55       ` Srinivas Pandruvada
2019-09-14 10:57   ` Quentin Perret
2019-09-17 14:27     ` Giovanni Gherdovich
2019-09-17 14:39       ` Quentin Perret
2019-09-24 14:03       ` Peter Zijlstra
2019-09-24 16:00         ` Peter Zijlstra
2019-10-02 12:27           ` Giovanni Gherdovich
2019-10-02 18:45             ` Peter Zijlstra [this message]
2019-09-24 16:04   ` Peter Zijlstra
2019-10-02 12:26     ` Giovanni Gherdovich
2019-10-02 18:35       ` Peter Zijlstra
2019-09-24 16:30   ` Peter Zijlstra
2019-10-02 12:25     ` Giovanni Gherdovich
2019-10-02 18:47       ` Peter Zijlstra
2019-09-09  2:42 ` [PATCH 2/2] cpufreq: intel_pstate: Conditional frequency invariant accounting Giovanni Gherdovich
2019-09-24 16:01 ` [PATCH 0/2] Add support for frequency invariance for (some) x86 Peter Zijlstra

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