Messages in this thread | | | Date | Tue, 27 Mar 2012 09:30:21 +1100 | Subject | Re: [ANNOUNCE] BFS CPU scheduler version 0.420 AKA "Smoking" for linux kernel 3.3.0 | From | Con Kolivas <> |
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On 26 March 2012 00:37, Mike Galbraith <efault@gmx.de> wrote: > Yeah. In all the interactivity testing I've ever done, it's really hard > to not see what you expect and/or hope to see. For normal desktop use, > I don't see any real difference with BFS vs CFS unless I load test of > course, and that can go either way, depending on the load. > > Example: > > 3.3.0-bfs vs 3.3.0-cfs - identical config > > Q6600 desktop box doing a measured interactivity test. > > time mplayer BigBuckBunny-DivXPlusHD.mkv, with massive_intr 8 as competition > > no bg load real 9m56.627s 1.000 > CFS real 9m59.199s 1.004 > BFS real 12m8.166s 1.220 > > As you can see, neither scheduler can run that perfectly on my box, as > the load needs a tad more than its fair share. However, the Interactive > Experience was far better in CFS in this case due to it being more fair. > In BFS, the interactive tasks (mplayer/Xorg) could not get their fair > share, causing interactivity to measurably suffer.
massive_intr runs a number of threads that each run for 8ms and then sleep for 1ms. That means they are 89% cpu bound. Run 8 of them and your CPU load is 88.8 * 8 = 7.1. So now you're testing a difficult mplayer benchmark in the presence of a load of 7.1 on a CPU with 4 cores. I don't know how much CPU the playback of your particular video is but I suspect it does require a fair amount of CPU based on the CPU it got back in your test. I can virtually guarantee that the amount of CPU BFS is giving to mplayer is proportional to how much CPU is left. Ergo as far as I can see, BFS is likely being absolutely perfectly fair. This sort of fairness equation has been already elucidated in the pHD that I linked to in my original post and he has done a much more thorough analysis than this kind of drive-by test that you're doing and misinterpreting has already shown that BFS is fair to a fault.
snip the rest
'top' snapshots are uninteresting because CFS and BFS report cpu time completely differently and a single snapshot tells us nothing.
Snip uninteresting-to-desktop-user throughput benchmarks. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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