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From: "Rafael J. Wysocki" <rjw@rjwysocki.net>
To: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
	Len Brown <lenb@kernel.org>, Linux PM <linux-pm@vger.kernel.org>,
	Vincent Guittot <vincent.guittot@linaro.org>,
	"v4 . 18+" <stable@vger.kernel.org>,
	Doug Smythies <doug.smythies@gmail.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH V3 2/2] cpufreq: intel_pstate: Implement ->resolve_freq()
Date: Fri, 02 Aug 2019 11:28:24 +0200	[thread overview]
Message-ID: <2676200.jfxhmTd764@kreacher> (raw)
In-Reply-To: <CAJZ5v0iqztRWyxf1cgiAN1dK4qTGwy9raaGOx5u3tfBTGUKOng@mail.gmail.com>

On Friday, August 2, 2019 11:17:55 AM CEST Rafael J. Wysocki wrote:
> On Fri, Aug 2, 2019 at 7:44 AM Viresh Kumar <viresh.kumar@linaro.org> wrote:
> >
> > Intel pstate driver exposes min_perf_pct and max_perf_pct sysfs files,
> > which can be used to force a limit on the min/max P state of the driver.
> > Though these files eventually control the min/max frequencies that the
> > CPUs will run at, they don't make a change to policy->min/max values.
> 
> That's correct.
> 
> > When the values of these files are changed (in passive mode of the
> > driver), it leads to calling ->limits() callback of the cpufreq
> > governors, like schedutil. On a call to it the governors shall
> > forcefully update the frequency to come within the limits.
> 
> OK, so the problem is that it is a bug to invoke the governor's ->limits()
> callback without updating policy->min/max, because that's what
> "limits" mean to the governors.
> 
> Fair enough.

AFAICS this can be addressed by adding PM QoS freq limits requests of each CPU to
intel_pstate in the passive mode such that changing min_perf_pct or max_perf_pct
will cause these requests to be updated.




  reply	other threads:[~2019-08-02  9:28 UTC|newest]

Thread overview: 10+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-02  5:44 [PATCH V3 1/2] cpufreq: schedutil: Don't skip freq update when limits change Viresh Kumar
2019-08-02  5:44 ` [PATCH V3 2/2] cpufreq: intel_pstate: Implement ->resolve_freq() Viresh Kumar
2019-08-02  9:17   ` Rafael J. Wysocki
2019-08-02  9:28     ` Rafael J. Wysocki [this message]
2019-08-03 15:00       ` Doug Smythies
2019-08-05  8:35         ` Rafael J. Wysocki
2019-08-06  4:10       ` Viresh Kumar
2019-08-06  8:05         ` Rafael J. Wysocki
2019-08-02  9:11 ` [PATCH V3 1/2] cpufreq: schedutil: Don't skip freq update when limits change Rafael J. Wysocki
2019-08-03  0:00   ` Doug Smythies

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