linux-kernel - lock's trace events can improve mutex's performance in userspace?

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Message-ID: <4B98BB50.1000002@cn.fujitsu.com>
Date:	Thu, 11 Mar 2010 17:43:44 +0800
From:	Xiao Guangrong <xiaoguangrong@...fujitsu.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Hitoshi Mitake <mitake@....info.waseda.ac.jp>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Ming Lei <tom.leiming@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: lock's trace events can improve mutex's performance in userspace?

We found that if enable lock's trace events, the 'sysbench mutex'
benchmark program can run quicker.

The simple program that is attached can reproduce it, the system info,
kernel config, and the script are also attached.

The test step is below:

# tar -zxvf test-mutex.tar.bz
# cd test-mutex
# make
# ./tscript.sh >& log
# cat log | grep "real"
real    0m46.765s < all trace events are disabled >
real    0m47.073s
real    0m47.402s
real    0m46.458s
real    0m47.433s
real    0m47.395s
real    0m47.010s
real    0m47.454s
real    0m47.044s
real    0m47.464s
real    0m39.245s < enable lock's trace events >
real    0m40.822s
real    0m40.779s
real    0m40.549s
real    0m40.605s
real    0m40.923s
real    0m40.560s
real    0m41.050s
real    0m40.757s
real    0m40.715s

[ "< ... >" is my comments ]

>From the result, we can see the program's runtime is less if enable lock's
trace events.

The conclusion is weird but i don't know why.

Download attachment "test-mutex.tar.bz" of type "application/octet-stream" (23996 bytes)