linux-kernel - Re: [PATCH v3] perf/record: add num-synthesize-threads option

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Date:   Thu, 23 Apr 2020 11:11:08 -0300
From:   Arnaldo Carvalho de Melo <arnaldo.melo@...il.com>
To:     Jiri Olsa <jolsa@...hat.com>
Cc:     Ian Rogers <irogers@...gle.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Mark Rutland <mark.rutland@....com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Kan Liang <kan.liang@...ux.intel.com>,
        Adrian Hunter <adrian.hunter@...el.com>,
        Alexey Budankov <alexey.budankov@...ux.intel.com>,
        yuzhoujian <yuzhoujian@...ichuxing.com>,
        Tony Jones <tonyj@...e.de>, linux-kernel@...r.kernel.org,
        linux-perf-users@...r.kernel.org,
        Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH v3] perf/record: add num-synthesize-threads option

Em Thu, Apr 23, 2020 at 02:09:57PM +0200, Jiri Olsa escreveu:
> On Wed, Apr 22, 2020 at 08:50:38AM -0700, Ian Rogers wrote:
> > From: Stephane Eranian <eranian@...gle.com>
> > 
> 
> SNIP
> 
> > That is the processing is 1.49% of execution time and there is plenty to
> > make parallel. This is shown in the benchmark in this patch:
> > https://lore.kernel.org/lkml/20200415054050.31645-2-irogers@google.com/
> > Computing performance of multi threaded perf event synthesis by
> > synthesizing events on CPU 0:
> >  Number of synthesis threads: 1
> >    Average synthesis took: 127729.000 usec (+- 3372.880 usec)
> >    Average num. events: 21548.600 (+- 0.306)
> >    Average time per event 5.927 usec
> >  Number of synthesis threads: 2
> >    Average synthesis took: 88863.500 usec (+- 385.168 usec)
> >    Average num. events: 21552.800 (+- 0.327)
> >    Average time per event 4.123 usec
> >  Number of synthesis threads: 3
> >    Average synthesis took: 83257.400 usec (+- 348.617 usec)
> >    Average num. events: 21553.200 (+- 0.327)
> >    Average time per event 3.863 usec
> >  Number of synthesis threads: 4
> >    Average synthesis took: 75093.000 usec (+- 422.978 usec)
> >    Average num. events: 21554.200 (+- 0.200)
> >    Average time per event 3.484 usec
> >  Number of synthesis threads: 5
> >    Average synthesis took: 64896.600 usec (+- 353.348 usec)
> >    Average num. events: 21558.000 (+- 0.000)
> >    Average time per event 3.010 usec
> >  Number of synthesis threads: 6
> >    Average synthesis took: 59210.200 usec (+- 342.890 usec)
> >    Average num. events: 21560.000 (+- 0.000)
> >    Average time per event 2.746 usec
> >  Number of synthesis threads: 7
> >    Average synthesis took: 54093.900 usec (+- 306.247 usec)
> >    Average num. events: 21562.000 (+- 0.000)
> >    Average time per event 2.509 usec
> >  Number of synthesis threads: 8
> >    Average synthesis took: 48938.700 usec (+- 341.732 usec)
> >    Average num. events: 21564.000 (+- 0.000)
> >    Average time per event 2.269 usec
> > 
> > Where average time per synthesized event goes from 5.927 usec with 1
> > thread to 2.269 usec with 8. This isn't a linear speed up as not all of
> > synthesize code has been made parallel. If the synthesis time was about
> > 10 seconds then using 8 threads may bring this down to less than 4.
> 
> Acked-by: Jiri Olsa <jolsa@...hat.com>

Thanks, applied.

- Arnaldo