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From: =?UTF-8?B?SsO2cmctVm9sa2VyIFBlZXR6?= <jvpeetz@web.de>
Subject: Re: [PATCH v2] proc:  speedup /proc/stat handling
Date: Mon, 30 Jan 2012 09:06:13 +0100
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Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
        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>
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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.