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    SubjectRe: [RFC PATCH] sched: START_NICE feature (temporarily niced forks) (v3)
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    On Tue, 2010-09-14 at 16:25 -0400, Mathieu Desnoyers wrote:
    > This patch tweaks the fair vruntime calculation of both the parent and the child
    > after a fork to double vruntime increment speed, but this is only applied to
    > their first slice after the fork. The goal of this scheme is that their
    > respective vruntime will increment faster in the first slice after the fork, so
    > a workload doing many forks (e.g. make -j10) will have a limited impact on
    > latency-sensitive workloads.
    >
    > This is an alternative to START_DEBIT which does not have the downside of moving
    > newly forked threads to the end of the runqueue.
    >
    > Changelog since v2:
    > - Apply vruntime penality even the first time the exec time has moved across
    > the timeout.
    >
    > Changelog since v1:
    > - Moving away from modifying the task weight from within the scheduler, as it is
    > error-prone: modifying the weight of a queued task leads to cpu weight errors.
    > For the moment, just tweak calc_delta_fair vruntime calculation. Eventually we
    > could revisit the weight modification approach if we decide that it's worth
    > the more intrusive changes. I redid the START_NICE benchmark, which did not
    > change much: it is still appealing.

    Some numbers from my Q6600 box, applied to v2.6.36-rc3-409-g3e6dce7.

    pinned wakeup-latency competing with pinned make -j10
    (taskset -c 3 ./wakeup-latency& sleep 30 && killall wakeup-latency)

    STOCK (ouch ouch ouch!, excellent testcase)
    maximum latency: 80558.8 µs 111838.0 µs 98196.6 µs
    average latency: 9682.4 µs 9357.8 µs 9559.0 µs
    missed timer events: 0 0 0

    NO_START_DEBIT
    maximum latency: 20015.5 µs 19247.8 µs 17204.2 µs
    average latency: 4923.0 µs 4985.2 µs 4879.5 µs
    missed timer events: 0 0 0

    START_NICE
    maximum latency: 19185.1 µs 19988.8 µs 19492.3 µs
    average latency: 4616.2 µs 4688.4 µs 4842.9 µs
    missed timer events: 0 0 0


    x264 8 threads (ultrafast)
    STOCK
    414.43 412.46 406.37 fps

    NO_START_DEBIT
    425.13 426.70 427.01 fps

    START_NICE
    423.80 424.87 419.00 fps


    pert (100% hog perturbation measurement proggy) competing with make -j3, 10 sec sample interval

    STOCK
    pert/s: 131 >16763.81us: 239 min: 0.15 max:54498.30 avg:5702.18 sum/s:746986us overhead:74.70%
    pert/s: 126 >18677.42us: 224 min: 0.13 max:65777.41 avg:6022.36 sum/s:761227us overhead:76.09%
    pert/s: 127 >20308.15us: 215 min: 0.11 max:64017.28 avg:5952.13 sum/s:757706us overhead:75.71%
    pert/s: 129 >21925.00us: 204 min: 0.41 max:67134.26 avg:5819.16 sum/s:752418us overhead:75.17% <== competition got

    NO_START_DEBIT
    pert/s: 113 >32566.80us: 140 min: 0.33 max:70870.38 avg:6937.03 sum/s:783885us overhead:78.39%
    pert/s: 112 >33261.53us: 127 min: 0.35 max:72063.85 avg:6964.25 sum/s:784871us overhead:78.40%
    pert/s: 111 >33372.61us: 112 min: 0.37 max:61722.37 avg:7022.35 sum/s:784397us overhead:78.44%
    pert/s: 112 >34183.11us: 115 min: 0.38 max:76023.87 avg:6931.32 sum/s:781853us overhead:78.19%

    START_NICE
    pert/s: 153 >20082.61us: 181 min: 0.06 max:52532.34 avg:4563.81 sum/s:702371us overhead:70.24%
    pert/s: 144 >21018.81us: 191 min: 0.14 max:53890.46 avg:4998.69 sum/s:722810us overhead:72.25%
    pert/s: 145 >22969.69us: 185 min: 0.12 max:76028.37 avg:5026.94 sum/s:729912us overhead:72.69%
    pert/s: 150 >23758.97us: 168 min: 0.12 max:56992.14 avg:4732.80 sum/s:709920us overhead:70.94%




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