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    SubjectRe: [RFC GIT PULL] perf/trace/lock optimization/scalability improvements
    On Wed, Feb 03, 2010 at 11:25:41AM +0100, Jens Axboe wrote:
    > On Wed, Feb 03 2010, Frederic Weisbecker wrote:
    > > Hi,
    > >
    > > There are many things that happen in this patchset, treating
    > > different problems:
    > >
    > > - remove most of the string copy overhead in fast path
    > > - open the way for lock class oriented profiling (as
    > > opposite to lock instance profiling. Both can be useful
    > > in different ways).
    > > - remove the buffers muliplexing (less contention)
    > > - event injection support
    > > - remove violent lock events recursion (only 2 among 3, the remaining
    > > one is detailed below).
    > >
    > > Some differences, by running:
    > > perf lock record perf sched pipe -l 100000
    > >
    > > Before the patchset:
    > >
    > > Total time: 91.015 [sec]
    > >
    > > 910.157300 usecs/op
    > > 1098 ops/sec
    > >
    > > After this patchset applied:
    > >
    > > Total time: 43.706 [sec]
    > >
    > > 437.062080 usecs/op
    > > 2288 ops/sec
    >
    > This does a lot better here, even if it isn't exactly stellar
    > performance. It generates a LOT of data:
    >
    > root@nehalem:/dev/shm # time perf lock rec -fg ls
    > perf.data perf.data.old
    > [ perf record: Woken up 0 times to write data ]
    > [ perf record: Captured and wrote 137.224 MB perf.data (~5995421
    > samples) ]



    Doh, 137 MB for a single ls :)

    That said we don't have yet support for callchains in perf lock,
    and callchains can fill the buffer quickly, especially on lock
    events. You can drop the -g option for now.


    >
    > real 0m3.320s
    > user 0m0.000s
    > sys 0m3.220s
    >
    > Without -g, it has 1.688s real and 1.590s sys time.


    Ok.


    > So while this is orders of magnitude better than the previous patchset,
    > it's still not anywhere near lean. But I expect you know that, just
    > consider this a 'I tested it and this is what happened' report :-)


    Ok, thanks a lot, the fact you can test on a 64 threads box is critically
    helpful.

    I also wonder what happens after this patch applied:

    diff --git a/kernel/perf_event.c b/kernel/perf_event.c
    index 98fd360..254b3d4 100644
    --- a/kernel/perf_event.c
    +++ b/kernel/perf_event.c
    @@ -3094,7 +3094,8 @@ static u32 perf_event_tid(struct perf_event *event, struct task_struct *p)
    if (event->parent)
    event = event->parent;

    - return task_pid_nr_ns(p, event->ns);
    + return p->pid;
    }

    In my box it has increased the speed from 2x this patchset.

    I wonder if the tool becomes usable for you with that.
    Otherwise, it means we have other things to fix, and
    the result of:
    perf record -g -f perf lock record sleep 6
    perf report

    would be very nice to have.

    Thanks!



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