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Date: Fri, 27 Feb 2009 12:13:10 -0800
Message-ID: <b040c32a0902271213q3dd1931foc2b955d8a028eb6f@mail.gmail.com>
Subject: Re: [PATCH] change cpuacct usage percpu format v2
From: Ken Chen <kenchen@google.com>
To: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
       "menage@google.com" <menage@google.com>,
       "lizf@cn.fujitsu.com" <lizf@cn.fujitsu.com>,
       "balbir@linux.vnet.ibm.com" <balbir@linux.vnet.ibm.com>, mingo@elte.hu,
       "akpm@linux-foundation.org" <akpm@linux-foundation.org>
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On Thu, Feb 26, 2009 at 11:29 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@jp.fujitsu.com> wrote:
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>
> cpuacct.usage_percpu shows per cpu usage information via cgroupfs.
> It shows all "present" cpus information and "whose information ?"
> is explained just by index of data implicitly.
>
> IIRC, there is physical cpu hotplug system and it can remove
> cpus and change map. Considering a software which records
> this information pediodically(like sar), its better to show id of cpu
> in explict way.

The new format carries a lot of overhead.  I would think user space
software can record /sys/devices/system/cpu/present and use that to
map cpu index.

- Ken