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SubjectRe: [PATCH] perf record: mmap output file - RFC

* David Ahern <dsahern@gmail.com> wrote:

> On 9/26/13 11:51 AM, Jiri Olsa wrote:
> >but it's still faster, since we finally get perf a chance to sleep ;-)
> >
> >new time:
> > real 0m30.392s
> > user 0m0.041s
> > sys 0m0.389s
> >
> >old time:
> > real 0m32.235s
> > user 0m3.080s
> > sys 0m14.444s
> >
>
> Another data point on the performance improvement of perf itself.
> Using openssl speed as a workload and perf-stat to collect
> information about the perf-record process only:
>
> perf stat -i -- perf record -g -o /tmp/perf.data openssl speed aes
>
> With write():
> 158.606380 task-clock
> 72 context-switches
> 34 cpu-migrations
> 5,400 page-faults
> 336,054,007 cycles
> 137,804,036 stalled-cycles-frontend
> 74,505,914 stalled-cycles-backend
> 474,401,639 instructions
> 91,246,072 branches
> 1,968,289 branch-misses
>
> With mmap():
> 50.314270 task-clock
> 61 context-switches
> 7 cpu-migrations
> 3,958 page-faults
> 93,585,618 cycles
> 64,878,225 stalled-cycles-frontend
> 41,680,427 stalled-cycles-backend
> 81,552,219 instructions
> 15,301,389 branches
> 387,230 branch-misses
>
> So time, CPU cycles, instructions all drop by more than a factor of 3.

Impressive!

Btw., a perf stat bugreport: it's not clear at all that 'task-clock' is in
units of milliseconds. Would be nice to print the unit as '(ms)' or so ...

For the other entries the unit is obvious (a count) - with the exception
of the task-clock.

Thanks,

Ingo


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