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Date: Wed, 25 Jan 2012 09:18:18 +0900 From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> To: Eric Dumazet <eric.dumazet@...il.com> Cc: Andrew Morton <akpm@...ux-foundation.org>, Glauber Costa <glommer@...allels.com>, Peter Zijlstra <a.p.zijlstra@...llo.nl>, Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org, Russell King - ARM Linux <linux@....linux.org.uk>, Paul Tuner <pjt@...gle.com> Subject: Re: [PATCH v2] proc: speedup /proc/stat handling On Wed, 25 Jan 2012 01:01:23 +0100 Eric Dumazet <eric.dumazet@...il.com> wrote: > On a typical 16 cpus machine, "cat /proc/stat" gives more than 4096 > bytes, and is slow : > > # strace -T -o /tmp/STRACE cat /proc/stat | wc -c > 5826 > # grep "cpu " /tmp/STRACE > read(0, "cpu 1949310 19 2144714 12117253"..., 32768) = 5826 <0.001504> > > > Thats partly because show_stat() must be called twice since initial > buffer size is too small (4096 bytes for less than 32 possible cpus) > > Fix this by : > > 1) Taking into account nr_irqs in the initial buffer sizing. > > 2) Using ksize() to allow better filling of initial buffer. > > > Signed-off-by: Eric Dumazet <eric.dumazet@...il.com> > Cc: Glauber Costa <glommer@...allels.com> > Cc: Russell King - ARM Linux <linux@....linux.org.uk> > Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> > Cc: Andrew Morton <akpm@...ux-foundation.org> > Cc: Paul Tuner <pjt@...gle.com> > Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl> > Cc: Ingo Molnar <mingo@...e.hu> Reviewed-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com> BTW, what is the reason of this change ? > - unsigned size = 4096 * (1 + num_possible_cpus() / 32); > + unsigned size = 1024 + 128 * num_possible_cpus(); I think size of buffer is affected by the number of online cpus. (Maybe 128 is enough but please add comment why 128 ?) And > size += 2 * nr_irqs; If this assumption fails, the issue comes again... -Kame -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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