linux-kernel - Re: [PATCH] proc/softirqs: only show state for online cpus

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Message-ID: <4E2E6102.3060600@jp.fujitsu.com>
Date:	Tue, 26 Jul 2011 15:38:58 +0900
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	yong.zhang0@...il.com
CC:	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
	kobayashi.kk@...s.nec.co.jp
Subject: Re: [PATCH] proc/softirqs: only show state for online cpus

(2011/07/26 15:14), Yong Zhang wrote:
> 2011/7/26 KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>:
>>> Like /proc/interrupts, no need to output data for nobody.
>>>
>>> Signed-off-by: Yong Zhang <yong.zhang0@...il.com>
>>> Cc: Andrew Morton <akpm@...ux-foundation.org>
>>> Cc: Keika Kobayashi <kobayashi.kk@...s.nec.co.jp>
>>> Cc: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
>>
>> If the cpu never be onlined, its statistics always 0. Then, it definitely
> 
> Yeah, so your screen may contain noise.

One question. Is this big matter?
Who see /proc/softirqs and /proc/interrupts directly? (i.e. by 'cat' command).


>> no value. In the other hand, if the cpu was offlined dynamically, we don't
>> know the user want to know the cpus's statistics or not.
> 
> Same to /proc/interrupts :)
> 
> IMHO, if user want to check the value of offline-cpu, maybe that means
> he want to check the state of the whole system, /proc/stat should be the
> right choice. /proc/{softirqs,interrupts} is just for immediate state.
>
>> Anyway, it's incompatibility change.
> 
> Yup, I should have marked the patch with RFC :)

And I should have remarked I don't dislike this patch so strongly, so
if kobayashi-san who original /proc/softirqs author ack you, I'm going
to second him.


Offtopic, /proc/interrupt should be protected by get_online_cpus().
Otherwise the header (i.e. cpu number) and the actual statistics fields
can be mismatched likes following. Am I missing something?

           CPU0       CPU1       CPU2
  0:   14286646   14747155          0   IO-APIC-edge      timer
  1:          6          6   IO-APIC-edge      i8042

                                 ^
                                 |
                               cpu2 was offlined dynamically at the same time.



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