linux-kernel - Re: [PATCH 17/19] perf tools: Always force PERF_RECORD_FINISHED

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Date:	Fri, 25 Jul 2014 13:34:26 +0200
From:	Jiri Olsa <jolsa@...hat.com>
To:	Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:	Jiri Olsa <jolsa@...nel.org>, linux-kernel@...r.kernel.org,
	Adrian Hunter <adrian.hunter@...el.com>,
	Corey Ashford <cjashfor@...ux.vnet.ibm.com>,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	Jean Pihet <jean.pihet@...aro.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Paul Mackerras <paulus@...ba.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH 17/19] perf tools: Always force
 PERF_RECORD_FINISHED_ROUND event

On Thu, Jul 24, 2014 at 06:34:51PM -0300, Arnaldo Carvalho de Melo wrote:
> Em Sun, Jul 20, 2014 at 11:56:01PM +0200, Jiri Olsa escreveu:
> > The PERF_RECORD_FINISHED_ROUND governs queue flushing in
> > reporting, so it needs to be stored for any kind of event.
> > 
> > Forcing the PERF_RECORD_FINISHED_ROUND event to be stored any
> > time we finish the round and wrote at least one event.
> 
> This is not just one change, it does two things and it is not clearly
> detailed here.
> 
> The existing code would write a PERF_RECORD_FINISHED_ROUND per call to
> record__mmap_read() for tracepoints were present.
> 
> I.e. if tracepoints and any other type of event type was present, then
> this syntetic PERF_RECORD_FINISHED_ROUND thing is inserted which will be
> handled at report time.
> 
> Now you changed it to not check if tracepoints are present, i.e. it will
> always insert that after processing N events in
> PERF_RECORD_FINISHED_ROUND. (change #1)
> 
> The thing is, before it didn't checked if N was zero, needlessly
> inserting PERF_RECORD_FINISHED_ROUND events in some corner cases.
> 
> Now you, in addition to change #1 you also check that the number of
> bytes written before that event processing loop in record__mmap_read()
> is the same after the loop, i.e. if some events were written to the
> output perf.data file, only inserting the PERF_RECORD_FINISHED_ROUND
> events if so. (change #2)
> 
> I think both changes are OK, but should be split in different patches,

right, I'll split it

> and while testing comparing having the patch applied versus patch
> applied + ignore the PERF_RECORD_FINISHED_ROUND events in the resulting
> perf.data file, I get:
> 
> [root@zoo /]# perf stat -r 5 perf report --no-ordered-samples > /dev/null
> <SNIP symbol stuff>
>  Performance counter stats for 'perf report --no-ordered-samples' (5 runs):
> 
>       30263.033852      task-clock (msec)         #    1.000 CPUs utilized            ( +-  0.48% )
>                346      context-switches          #    0.011 K/sec                    ( +- 54.65% )
>                182      cpu-migrations            #    0.006 K/sec                    ( +- 29.94% )
>             89,951      page-faults               #    0.003 M/sec                    ( +-  0.05% )
>     92,342,939,311      cycles                    #    3.051 GHz                      ( +-  0.46% )
>     50,605,250,178      stalled-cycles-frontend   #   54.80% frontend cycles idle     ( +-  0.88% )
>    <not supported>      stalled-cycles-backend   
>    101,171,572,553      instructions              #    1.10  insns per cycle        
>                                                   #    0.50  stalled cycles per insn  ( +-  0.01% )
>     22,643,469,804      branches                  #  748.222 M/sec                    ( +-  0.01% )
>        284,395,273      branch-misses             #    1.26% of all branches          ( +-  0.45% )
> 
>       30.249514999 seconds time elapsed                                          ( +-  0.48% )
> 
> [root@zoo /]# perf stat -r 5 perf report --ordered-samples > /dev/null
> <SNIP symbol stuff>
>  Performance counter stats for 'perf report --ordered-samples' (5 runs):
> 
>       32665.828429      task-clock (msec)         #    1.001 CPUs utilized            ( +-  0.41% )
>                304      context-switches          #    0.009 K/sec                    ( +- 23.32% )
>                102      cpu-migrations            #    0.003 K/sec                    ( +- 21.70% )
>             79,405      page-faults               #    0.002 M/sec                    ( +-  0.02% )
>    101,761,091,322      cycles                    #    3.115 GHz                      ( +-  0.40% )
>     57,627,138,326      stalled-cycles-frontend   #   56.63% frontend cycles idle     ( +-  0.65% )
>    <not supported>      stalled-cycles-backend   
>    105,982,144,263      instructions              #    1.04  insns per cycle        
>                                                   #    0.54  stalled cycles per insn  ( +-  0.01% )
>     23,493,670,235      branches                  #  719.212 M/sec                    ( +-  0.01% )
>        319,060,575      branch-misses             #    1.36% of all branches          ( +-  0.19% )
> 
>       32.636483981 seconds time elapsed                                          ( +-  0.41% )
> 
> [root@zoo /]#

so those 2 extra seconds is the ordering time, right? sounds ok

jirka
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