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    SubjectRe: BFS vs. mainline scheduler benchmarks and measurements
    On Wed, Sep 09 2009, Nikos Chantziaras wrote:
    > 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?

    It probably just means that latt isn't a good measure of the problem.
    Which isn't really too much of a surprise.

    --
    Jens Axboe



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