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    SubjectRe: [ANNOUNCE] BFS CPU scheduler version 0.420 AKA "Smoking" for linux kernel 3.3.0
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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.
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