Re: [PATCH v2] proc: speedup /proc/stat handling

[Andrew Morton]

On Wed, 25 Jan 2012 01:22:25 +0100
Eric Dumazet <eric.dumazet@xxxxxxxxx> wrote:

> Le mardi 24 janvier 2012 __ 16:12 -0800, Andrew Morton a __crit :
> 
> > Did you measure the improvement from this patch?
> 
> Unfortunately I can not reboot the server where I noticed this
> performance problem.
> 
> On the smaller one, performance improvement is about 20%, because the
> second run of show_stat() can use data present in cpu cache.
> 
> On big machines, I guess the 128 bytes per possible cpu reservation can
> avoid the second run. (since a typical cpuXXX line is smaller than 128
> bytes)

I had a fiddle on an 8-way x86_64 machine.  I'm unable to demonstrate
any improvement for either of

time (for i in $(seq 1000); do; cat /proc/self/stat > /dev/null; done)
time (for i in $(seq 1000); do; cat /proc/1/stat > /dev/null; done)

oh well.
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