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From: David Ahern <dsahern@gmail.com>
To: Namhyung Kim <namhyung@kernel.org>
Cc: acme@ghostprotocols.net, linux-kernel@vger.kernel.org,
	Ingo Molnar <mingo@kernel.org>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Jiri Olsa <jolsa@redhat.com>, Mike Galbraith <efault@gmx.de>,
	Stephane Eranian <eranian@google.com>
Subject: Re: [PATCH] perf record: mmap output file - v2
Date: Tue, 15 Oct 2013 19:58:34 -0600	[thread overview]
Message-ID: <525DF2CA.1060102@gmail.com> (raw)
In-Reply-To: <87haci9e31.fsf@sejong.aot.lge.com>

On 10/15/13 7:52 PM, Namhyung Kim wrote:
> Aha, okay.  So it mostly matters to syscall tracing, right?  For a
> normal record session, it seems that the effect is not that large:

Yes, that's in the description "When recording raw_syscalls for the 
entire system"

There is a small benefit to all record sessions -- mmap+memcpy has less 
overhead than write(). I still need to look at Ingo's suggestion to use 
non-temporal stores which might reduce the overhead of the memcpy.

Try a workload that generates a HUGE data file -- say a full kernel 
build (e.g., perf record -g -- make O=/tmp/kbuild -j 16). You should see 
a much larger benefit from the mmap route. Be sure to use your callchain 
enhancements to look at that 1+G file. ;-)

David

      reply	other threads:[~2013-10-16  1:58 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2013-10-15  2:55 [PATCH] perf record: mmap output file - v2 David Ahern
2013-10-15  6:02 ` Ingo Molnar
2013-10-15  7:09   ` Namhyung Kim
2013-10-15  7:25     ` Ingo Molnar
2013-10-15  8:17       ` Namhyung Kim
2013-10-15 12:22       ` Jiri Olsa
2013-10-15 13:20         ` Ingo Molnar
2013-10-15 13:25     ` David Ahern
2013-10-16  1:24       ` Namhyung Kim
2013-10-15  7:31 ` Namhyung Kim
2013-10-15  7:44   ` Ingo Molnar
2013-10-15 13:45     ` David Ahern
2013-10-15 13:35   ` David Ahern
2013-10-16  1:52     ` Namhyung Kim
2013-10-16  1:58       ` David Ahern [this message]

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