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

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Date:	Mon, 30 Jan 2012 09:06:13 +0100
From:	Jörg-Volker Peetz <jvpeetz@....de>
To:	linux-kernel@...r.kernel.org
Cc:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	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

Eric Dumazet wrote, on 01/25/12 01:26:
> Le mercredi 25 janvier 2012 à 09:18 +0900, KAMEZAWA Hiroyuki a écrit :
> 
>> 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 ?)
>>
> 
> There is no change, as 4096/32 is 128 bytes per cpu.
> 

Wrong math, only num_possible_cpus() is divided by 32. Thus,

-	unsigned size = 4096 * (1 + num_possible_cpus() / 32);
+	unsigned size = 4096 + 128 * num_possible_cpus();

<snip>
-- 
Best regards,
Jörg-Volker.

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