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    SubjectRe: [RFC GIT PULL] perf/trace/lock optimization/scalability improvements
    On Wed, Feb 03 2010, Frederic Weisbecker wrote:
    > 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 :)

    Yeah, it's pretty crazy. It varies a lot too, I didn't post the other
    run which was ~170MB.

    > 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.

    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.

    My pleasure, I'd love to have a fast and functional perf lockstat. If my
    testing helps getting there, consider me signed up :-)

    > 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.

    Cool, I'll give that a spin in the morning, the box is off atm.

    > 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.

    I'll package that up for you and put it somewhere.

    --
    Jens Axboe



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