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Date: Thu, 26 Jan 2012 17:18:00 -0800
From: Andrew Morton <akpm@linux-foundation.org>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Eric Dumazet <eric.dumazet@gmail.com>,
        Glauber Costa <glommer@parallels.com>,
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        linux-kernel@vger.kernel.org,
        Russell King - ARM Linux <linux@arm.linux.org.uk>,
        Paul Tuner <pjt@google.com>
Subject: Re: [PATCH v2] proc:  speedup /proc/stat handling
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On Fri, 27 Jan 2012 10:09:33 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote:

> > I expect most of these numbers are zero.  I wonder if we would get
> > useful speedups from
> > 
> > 	for_each_irq_nr(j) {
> > 		/* Apologetic comment goes here */
> > 		if (kstat_irqs(j))
> > 			seq_printf(p, " %u", kstat_irqs(j));
> > 		else
> > 			seq_puts(p, " 0");
> > 	}
> 
> Yes. This is very good optimization and shows much optimization.
> I did this at first try  but did complicated ones because it seems
> not interesting. (This is my bad habit...)
> 
> I'll try again and measure time.

seq_puts() is too slow ;)  I bet seq_putc(p, ' ');seq_putc(p, '0') will
complete in negative time.