Re: [RFC GIT PULL] perf/trace/lock optimization/scalability improvements

[Frederic Weisbecker <fweisbec@gmail.com>]

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!