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. TL:RD: run the very same test multiple times without any changes and you get "vastly" different results. And just from these coarse statistics it's hard to judge whether especially min/max have any significance anyway. That's why you usually also include deviation/variance when writing performance tests, and some percentiles if you have enough individual measurements and the means to store those. What you _can_ tell from these numbers is that the spread for a single function and run is in the percents. 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. Regards, Julian [1]: https://github.com/patchew-project/qemu/tree/patchew/[email protected]
