linux-kernel - Re: [PATCH] change cpuacct usage percpu format v2

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Date:	Fri, 27 Feb 2009 12:13:10 -0800
From:	Ken Chen <kenchen@...gle.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"menage@...gle.com" <menage@...gle.com>,
	"lizf@...fujitsu.com" <lizf@...fujitsu.com>,
	"balbir@...ux.vnet.ibm.com" <balbir@...ux.vnet.ibm.com>,
	mingo@...e.hu,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [PATCH] change cpuacct usage percpu format v2

On Thu, Feb 26, 2009 at 11:29 PM, KAMEZAWA Hiroyuki
<kamezawa.hiroyu@...fujitsu.com> wrote:
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...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
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