linux-kernel - Re: [PATCH] perf record: mmap output file

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Message-ID: <5244C09B.7040500@gmail.com>
Date:	Thu, 26 Sep 2013 17:17:47 -0600
From:	David Ahern <dsahern@...il.com>
To:	Jiri Olsa <jolsa@...hat.com>, acme@...stprotocols.net
CC:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Mike Galbraith <efault@....de>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH] perf record: mmap output file - RFC

On 9/26/13 11:51 AM, Jiri Olsa wrote:
> but it's still faster, since we finally get perf a chance to sleep ;-)
>
> new time:
> 	real    0m30.392s
> 	user    0m0.041s
> 	sys     0m0.389s
>
> old time:
> 	real    0m32.235s
> 	user    0m3.080s
> 	sys     0m14.444s
>

Another data point on the performance improvement of perf itself. Using 
openssl speed as a workload and perf-stat to collect information about 
the perf-record process only:

perf stat -i -- perf record -g -o /tmp/perf.data openssl speed aes

With write():
        158.606380 task-clock
                 72 context-switches
                 34 cpu-migrations
              5,400 page-faults
        336,054,007 cycles
        137,804,036 stalled-cycles-frontend
         74,505,914 stalled-cycles-backend
        474,401,639 instructions
         91,246,072 branches
          1,968,289 branch-misses

With mmap():
         50.314270 task-clock
                 61 context-switches
                  7 cpu-migrations
              3,958 page-faults
         93,585,618 cycles
         64,878,225 stalled-cycles-frontend
         41,680,427 stalled-cycles-backend
         81,552,219 instructions
         15,301,389 branches
            387,230 branch-misses

So time, CPU cycles, instructions all drop by more than a factor of 3.

David
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