On Thu, Jun 13, 2019 at 10:12 AM Pavel Machek <pavel@xxxxxx> wrote: > > Hi! > > > 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 > > 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!
