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    SubjectRe: BFS vs. mainline scheduler benchmarks and measurements
    On 09/09/2009 09:04 PM, Ingo Molnar wrote:
    > [...]
    > * Jens Axboe<jens.axboe@oracle.com> wrote:
    >
    >> On Wed, Sep 09 2009, Jens Axboe wrote:
    >> [...]
    >> BFS210 runs on the laptop (dual core intel core duo). With make -j4
    >> running, I clock the following latt -c8 'sleep 10' latencies:
    >>
    >> -rc9
    >>
    >> Max 17895 usec
    >> Avg 8028 usec
    >> Stdev 5948 usec
    >> Stdev mean 405 usec
    >>
    >> Max 17896 usec
    >> Avg 4951 usec
    >> Stdev 6278 usec
    >> Stdev mean 427 usec
    >>
    >> Max 17885 usec
    >> Avg 5526 usec
    >> Stdev 6819 usec
    >> Stdev mean 464 usec
    >>
    >> -rc9 + mike
    >>
    >> Max 6061 usec
    >> Avg 3797 usec
    >> Stdev 1726 usec
    >> Stdev mean 117 usec
    >>
    >> Max 5122 usec
    >> Avg 3958 usec
    >> Stdev 1697 usec
    >> Stdev mean 115 usec
    >>
    >> Max 6691 usec
    >> Avg 2130 usec
    >> Stdev 2165 usec
    >> Stdev mean 147 usec
    >
    > At least in my tests these latencies were mainly due to a bug in
    > latt.c - i've attached the fixed version.
    >
    > The other reason was wakeup batching. If you do this:
    >
    > echo 0> /proc/sys/kernel/sched_wakeup_granularity_ns
    >
    > ... then you can switch on insta-wakeups on -tip too.
    >
    > With a dual-core box and a make -j4 background job running, on
    > latest -tip i get the following latencies:
    >
    > $ ./latt -c8 sleep 30
    > Entries: 656 (clients=8)
    >
    > Averages:
    > ------------------------------
    > Max 158 usec
    > Avg 12 usec
    > Stdev 10 usec

    With your version of latt.c, I get these results with 2.6-tip vs
    2.6.31-rc9-bfs:


    (mainline)
    Averages:
    ------------------------------
    Max 50 usec
    Avg 12 usec
    Stdev 3 usec


    (BFS)
    Averages:
    ------------------------------
    Max 474 usec
    Avg 11 usec
    Stdev 16 usec


    However, the interactivity problems still remain. Does that mean it's
    not a latency issue?


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