Re: 5.2-rc2: low framerate in flightgear, cpu not running at full speed, thermal related?
From: Pavel Machek
Date: Thu Jun 13 2019 - 12:37:53 EST
> On 2019.06.12 14:25 Rafael J. Wysocki wrote:
> > On Wed, Jun 12, 2019 at 4:45 AM Doug Smythies <dsmythies@xxxxxxxxx> 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
It seems there are serious differences in reporting :-(. How do I
determine which frequency CPU really runs at, in 4.6 kernel?
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?
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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