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Subject: Re: [PATCH v2] proc:  speedup /proc/stat handling
From: Eric Dumazet <eric.dumazet@gmail.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Glauber Costa <glommer@parallels.com>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>, Ingo Molnar <mingo@elte.hu>,
        linux-kernel@vger.kernel.org,
        Russell King - ARM Linux <linux@arm.linux.org.uk>,
        Paul Tuner <pjt@google.com>
Date: Fri, 27 Jan 2012 08:09:07 +0100
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Le vendredi 27 janvier 2012 à 10:09 +0900, KAMEZAWA Hiroyuki a écrit :
> On Thu, 26 Jan 2012 16:43:42 -0800
> Andrew Morton <akpm@linux-foundation.org> 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.
> 

Also make it generic maybe, and evaluate kstat_irqs(i) once.

seq_put_u32(struct seq_file *m, u32 val);

Converting an "u32" to its decimal representation should be fast, even
for non zero values. Many other users could benefit from this.