linux-kernel - Re: [PATCH 5/7] perf tools: Optimize sample parsing for ordered events

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Date:   Tue, 31 Oct 2017 10:40:54 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Jiri Olsa <jolsa@...nel.org>
Cc:     Arnaldo Carvalho de Melo <acme@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Namhyung Kim <namhyung@...nel.org>,
        David Ahern <dsahern@...il.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 5/7] perf tools: Optimize sample parsing for ordered
 events


* Jiri Olsa <jolsa@...nel.org> wrote:

> Currently when using ordered events we parse the sample
> twice (the perf_evlist__parse_sample function). Once
> before we queue the sample for sorting:
> 
>   perf_session__process_event
>     perf_evlist__parse_sample(sample)
>     perf_session__queue_event(sample.time)
> 
> And then when we deliver the sorted sample:
> 
>   ordered_events__deliver_event
>     perf_evlist__parse_sample
>     perf_session__deliver_event
> 
> We can skip the initial full sample parsing by using
> perf_evlist__parse_sample_timestamp function, which
> got introduced earlier. The new path looks like:
> 
>   perf_session__process_event
>     perf_evlist__parse_sample_timestamp
>     perf_session__queue_event
> 
>   ordered_events__deliver_event
>     perf_session__deliver_event
>       perf_evlist__parse_sample
> 
> It saves some instructions and is slightly faster:
> 
> Before:
>  Performance counter stats for './perf.old report --stdio' (5 runs):
> 
>     64,396,007,225      cycles:u                                                      ( +-  0.97% )
>    105,882,112,735      instructions:u            #    1.64  insn per cycle           ( +-  0.00% )
> 
>       21.618103465 seconds time elapsed                                          ( +-  1.12% )
> 
> After:
>  Performance counter stats for './perf report --stdio' (5 runs):
> 
>     60,567,807,182      cycles:u                                                      ( +-  0.40% )
>    104,853,333,514      instructions:u            #    1.73  insn per cycle           ( +-  0.00% )
> 
>       20.168895243 seconds time elapsed                                          ( +-  0.32% )

That's a 7% speedup, not bad!

Thanks,

	Ingo