Re: [PATCH 1/3] perf tools: Record total sampling time

[Ingo Molnar <mingo@kernel.org>]

So basically, in the end I think it should be possible to have the 
following behavior:

   perf record -a -e cycles sleep 1

   perf report stat              # Reports as if we ran: 'perf stat -a -e cycles sleep 1'
   perf report                   # Reports the usual histogram

   perf report --stat            # Reports the perf stat output and the histogram

or so.

i.e. a perf.data file would by default always carry enough information 
to enable the extraction of the 'perf stat' data.

At that point visualizing it is purely report-time logic, it does not 
need any record-time options.

This would work for multi-event sampling as well, if we do:

   perf record -a -e cycles -e branches sleep 1

then 'perf report stat' would output the same as:

 $ perf stat -e cycles -e branches -a sleep 1

 Performance counter stats for 'system wide':

        34,174,518      cycles                    [100.00%]
         3,155,677      branches                                                    

       1.000802852 seconds time elapsed

Another neat feature this kind of workflo enables is the integration 
of --repeat to perf record, so something like:

    perf record --repeat 3 -a -e cycles -e branches sleep 1

would save 3 samples after each other, and would allow extraction of 
the statistical stability of the measurement, and 'perf report stat' 
would print the same result as a raw perf stat run would:

 $ perf stat --repeat 3 -e cycles -e branches -e instructions -a sleep 1

 Performance counter stats for 'system wide' (3 runs):

    28,975,150,642      cycles                     ( +-  0.43% ) [100.00%]
    10,740,235,371      branches                                                      ( +-  0.47% ) [100.00%]
    44,535,464,754      instructions              #    1.54  insns per cycle          ( +-  0.47% )

       1.005718027 seconds time elapsed                                          ( +-  0.43% )

Or something like that. At that point we share reporting between perf 
stat and perf report, no special ad-hoc options are needed to just 
measure and report timestamps, it would all be a 'natural' side effect 
of having perf stat.

What do you think?

Thanks,

	Ingo