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From: "Rafael J. Wysocki" <rafael@kernel.org>
To: Pavel Machek <pavel@ucw.cz>
Cc: Doug Smythies <dsmythies@telus.net>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	kernel list <linux-kernel@vger.kernel.org>,
	ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
	"Zhang, Rui" <rui.zhang@intel.com>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Viresh Kumar <viresh.kumar@linaro.org>,
	Linux PM <linux-pm@vger.kernel.org>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"the arch/x86 maintainers" <x86@kernel.org>
Subject: Re: 5.2-rc2: low framerate in flightgear, cpu not running at full speed, thermal related?
Date: Thu, 13 Jun 2019 11:00:29 +0200
Message-ID: <CAJZ5v0hLPWsVzgRUT3_tZ6day6GzaxW2HWrK7RMaXLfpjwraOA@mail.gmail.com> (raw)
In-Reply-To: <20190613081158.GA6853@amd>

On Thu, Jun 13, 2019 at 10:12 AM Pavel Machek <pavel@ucw.cz> wrote:
>
> Hi!
>
> > On 2019.06.12 14:25 Rafael J. Wysocki wrote:
> > > On Wed, Jun 12, 2019 at 4:45 AM Doug Smythies <dsmythies@telus.net> wrote:
> > >>
> > >> So, currently there seems to be 3 issues in this thread
> > >> (and I am guessing a little, without definitive data):
> > >>
> > >> 1.) On your system Kernel 5.4-rc2 (or 4) defaults to the intel_pstate CPU frequency
> > >> scaling driver and the powersave governor, but kernel 4.6 defaults to the
> > >> acpi-cpufreq CPU frequency scaling driver and the ondemand governor.
> > >
> > > Which means that intel_pstate works in the active mode by default and
> > > so it uses its internal governor.
> >
> > Note sure what you mean by "internal governor"?
> > If you meant HWP (Hardware P-state), Pavel's processor doesn't have it.
> > If you meant the active powersave governor code within the driver, then agreed.
> >
> > > That governor is more performance-oriented than ondemand and it very
> > > well may cause more power to be allocated for the processor - at the
> > > expense of the GPU.
> >
> > O.K. I mainly use servers and so have no experience with possible GPU
> > verses CPU tradeoffs.
> >
> > However, I did re-do my tests measuring energy instead of CPU frequency
> > and found very little difference between the acpi-cpufreq/ondemand verses
> > intel_pstate/powersave as a function of single threaded load. Actually,
> > I did the test twice, one at 20 hertz work/sleep frequency and also
> > at 67 hertz work/sleep frequency. (Of course, Pavel's processor might
> > well have a different curve, but it is a similar vintage to mine
> > i5-2520M verses i7-2600K.) The worst difference was approximately
> > 1.1 extra processor package watts (an extra 5.5%) in the 80% to 85%
> > single threaded load range at 67 hertz work/sleep frequency for
> > the intel-pstate/powersave driver/governor.
> >
> > What am I saying? For a fixed amount of work to do per work/sleep cycle
> > (i.e. maybe per video frame related type work) while the CPU frequency Verses load
> > curves might differ, the resulting processor energy curve differs much less.
> > (i.e. the extra power for higher CPU frequency is for less time because it gets
> > the job done faster.) So, myself, I don't yet understand why only the one method
> > would have hit thermal throttling, but not the other (if indeed it
> > doesn't).
>
> It seems there are serious differences in reporting :-(. How do I
> determine which frequency CPU really runs at, in 4.6 kernel?

With that kernel (and the acpi-cpufreq driver) the only way is to run
your workload under turbostat.

> But it seems that your assumptions are incorrect for my workload.
>
> flightgear is single-threaded, and in my configuration saturates the
> CPU, because it would like to achieve higher framerate than my system
> is capable of.
>
> > Just for information: CPU frequency verses single threaded load curves
> > for the conservative governor is quite different between the two drivers.
> > (tests done in February, perhaps I should re-do and also look at energy
> > at the same time, or instead of CPU frequency.)
>
> So this might be my problem?

Not really, because you don't use the conservative governor. :-)

Generally, I agree with Doug that CPU performance scaling is unlikely
to be the source of the symptom that you are observing.

Anyway, if you did what I had said previously (ie. run intel_pstate in
the passive mode and use ondemand as the governor) and still see
reduced frame rate (with respect to 4.6), that would basically rule
CPU performance scaling out.

Cheers!

  reply index

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-09 11:17 Pavel Machek
2019-06-09 11:23 ` Pavel Machek
2019-06-09 12:12   ` Pavel Machek
2019-06-09 13:55     ` Daniel Lezcano
2019-06-09 14:13     ` Zhang Rui
2019-06-11 10:12       ` Pavel Machek
2019-06-11 10:15         ` Viresh Kumar
2019-06-12  2:37 ` Doug Smythies
2019-06-12 21:44   ` Rafael J. Wysocki
2019-06-12 23:39     ` Doug Smythies
2019-06-13  8:11       ` Pavel Machek
2019-06-13  9:00         ` Rafael J. Wysocki [this message]
2019-06-13  8:52       ` Rafael J. Wysocki
2019-06-18  8:20         ` Doug Smythies
2019-06-18  8:34           ` Pavel Machek

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