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SubjectRe: Tracing configuration review
On Wed, May 26, 2010 at 01:06:57AM +0200, Frederic Weisbecker wrote:
> On Tue, May 25, 2010 at 05:09:59PM -0400, Chase Douglas wrote:
> > On Tue, 2010-05-25 at 22:13 +0200, Frederic Weisbecker wrote:
> > > On Tue, May 25, 2010 at 03:31:46PM -0400, Chase Douglas wrote:

<snipped>

> > > IMO, it is deprecated. The perf interface is much more powerful and flexible.
> > > Prasad, do you agree if I remove this ftrace plugin?

Sure, go ahead.

> >
> > If there isn't any use in enabling it due to perf's features, then we
> > can turn it off. However, if there's any use to be gained by this over
> > perf's features, then I'd prefer to leave it on. Thoughts?
>
>
>
> No, perf does much more:
>
> - stacktraces recording
> - "top" alike view with perf top
> - stat with perf stat, etc...
> - userspace memory accesses
>
>
> Here is a quick example:
>
> $ cat test.c
> int var;
>
> void func_c(void)
> {
> var++;
> }
>
> void func_b(void)
> {
> func_c();
> }
>
>
> void func_a(void)
> {
> func_c();
> }
>
>
> int main(int argc, char **argv)
> {
> int i;
>
> for (i = 0; i < 1000; i++)
> if (i % 2)
> func_a();
> else
> func_b();
>
> return 0;
> }
> //end test.c
>
> $ gcc test.c -fno-omit-frame-pointer -o test
>
> $ readelf -s test | grep var
> 74: 000000000060102c 4 OBJECT GLOBAL DEFAULT 25 var
>
> $ perf record -g -c 1 -e mem:0x000000000060102c:w ./test
> [ perf record: Woken up 1 times to write data ]
> [ perf record: Captured and wrote 0.069 MB perf.data (~3020 samples) ]
>
> $ perf report
>
> # Events: 1K cycles
> #
> # Overhead Command Shared Object Symbol
> # ........ ....... ................. ......
> #
> 99.90% test test [.] func_c
> |
> --- func_c
> |
> |--49.95%-- func_a
> | |
> | |--99.60%-- main
> | | __libc_start_main
> | --0.40%-- [...]
> |
> |--49.85%-- func_b
> | main
> | |
> | |--99.60%-- __libc_start_main
> | --0.40%-- [...]
> --0.20%-- [...]
>
>
> To sum up, there is nothing the ksym tracer does that perf can't.
>

I second Frederic's opinion on this.

Thanks,
K.Prasad

> Well, may be perf doesn't offer the time ordered view of memory
> accesses, I must confess. Although this is still something we can
> easily provide if people want it.
>


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