2013-12-02 (월), 13:57 +0100, Ingo Molnar:
> 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 don't think we need both of 'perf report stat' and 'perf report
--stat'. At least it looks somewhat confusing to users IMHO.
For perf report stat usage, I think there's not much thing we can do for
a single event - the most case. We can simple show total count and
elapsed (or sampled time) for the event, but it's already in the header
with this patch.
# Samples: 4K of event 'cycles'
# Event count (approx.): 4087481688
# Total sampling time : 1.001260 (sec)
If an user really want to see perf stat-like output (without the usual
histogram) for a recorded session, it'd be better to have 'perf record
--stat' do the job (like git diff --stat) IMHO.
>
> 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
>
Yeah, it'd be good to have same output both for perf stat and perf
report --stat (or stat if you want). But I don't think it's possible to
determine multiplexed counter values like perf stat does unless we use
PERF_SAMPLE_READ for recoding.
> 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% )
Yeah, but it can be used only for a new forked workload.
>
> 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?
I think it'd be better if we can share code as much as possible. And
it'd much better if we can forget about the difference in options. :)
Thanks,
Namhyung
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