linux-kernel - Re: [PATCH v2] proc: speedup /proc/stat handling

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Message-Id: <20120126171800.01c2405c.akpm@linux-foundation.org>
Date:	Thu, 26 Jan 2012 17:18:00 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Eric Dumazet <eric.dumazet@...il.com>,
	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 Fri, 27 Jan 2012 10:09:33 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@...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.
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