"Julian Ganz" <neither@nut.email> writes: > September 10, 2025 at 12:06 PM, "BALATON Zoltan" wrote: >> On Tue, 9 Sep 2025, Julian Ganz wrote: >> > I ran streamPPCpowerpcO3 on qemu with these patches: >> > >> > ------------------------------------------------------------- >> > Function Best Rate MB/s Avg time Min time Max time >> > Copy: 2867.6 0.056828 0.055795 0.061792 >> > Scale: 1057.5 0.153282 0.151305 0.158115 >> > Add: 1308.8 0.187095 0.183380 0.193672 >> > Triad: 1111.6 0.220863 0.215902 0.230440 >> > ------------------------------------------------------------- >> > >> > After doing a clean build, with the fans still audible: >> > >> > ------------------------------------------------------------- >> > Function Best Rate MB/s Avg time Min time Max time >> > Copy: 2932.9 0.055131 0.054554 0.055667 >> > Scale: 1067.9 0.151520 0.149832 0.155000 >> > Add: 1324.9 0.184807 0.181150 0.191386 >> > Triad: 1122.0 0.220080 0.213896 0.229302 >> > ------------------------------------------------------------- >> > >> What was different between the above two runs? I guess maybe one is with >> plugins disabled but it's not clear from the description. > > The difference is nothing but a a clean rebuild of qemu. As you see > there are fluctuations already. Plugins are enabled for both cases. > >> > On qemu (6a9fa5ef3230a7d51e0d953a59ee9ef10af705b8) without these >> > patches, but plugins enabled: >> > >> > ------------------------------------------------------------- >> > Function Best Rate MB/s Avg time Min time Max time >> > Copy: 2972.1 0.054407 0.053834 0.054675 >> > Scale: 1068.6 0.151503 0.149726 0.154594 >> > Add: 1327.6 0.185160 0.180784 0.193181 >> > Triad: 1127.2 0.219249 0.212915 0.229230 >> > ------------------------------------------------------------- >> > >> > And on qemu (6a9fa5ef3230a7d51e0d953a59ee9ef10af705b8) without these >> > patches, with plugins disabled: >> > >> > ------------------------------------------------------------- >> > Function Best Rate MB/s Avg time Min time Max time >> > Copy: 2983.4 0.055141 0.053630 0.060013 >> > Scale: 1058.3 0.152353 0.151186 0.155072 >> > Add: 1323.9 0.184707 0.181279 0.188868 >> > Triad: 1128.2 0.218674 0.212734 0.230314 >> > ------------------------------------------------------------- >> > >> > I fail to see any significant indication that these patches, or >> > plugins in general, would result in a degredation of performance. >> > >> With worst case Copy test it seems to be about 3.5% (and about 1.7% >> with plugins disabled?) and should be less than that normally so it >> does not add much more overhead to plugins than there is already so >> this should be acceptable. It may still be interesting to see if the >> overhead with plugins disabled can be avoided with a similar way as >> logging does it. > > The thing is: that's probably just usual fluctuations. As you have seen > with the first two measurements the values fluctuate quite a bit between > runs of the test on the very same qemu (assuming that a clean build did > not incur any _other_ relevant change). For example, the best rate for > scale shown with plugins enabled is one percent faster than with plugins > disabled. Is this significant? Probably not. Or at least it doesn't make > much sense.
I wouldn't spend too much time chasing this down. As you say this fluctuation is well within the noise range. I can recommend hyperfine as a runner: https://github.com/sharkdp/hyperfine as it does some work on how many times you need to run a test before the results are statistically relevant. > I may do some more tests this week, with runtimes longer than a few > seconds if I can find the motivation to set up everything I'd need to > compile your benchmark. In the mean-time, you are welcome to make your > own measurements if you want to. The patches are also availible at [1] > if you don't want to apply them to your local tree yourself. Balton, I don't think worries about performance impact are justified and Julian has certainly done enough due diligence here. If you can come up with a repeatable test that shows a measurable impact then please do so. > > Regards, > Julian > > [1]: > https://github.com/patchew-project/qemu/tree/patchew/cover.1757018626.git.neither@nut.email -- Alex Bennée Virtualisation Tech Lead @ Linaro
