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Subjectlock'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
# cd test-mutex
# make
# ./ >& 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.
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