linux-kernel - Re: [RFD PATCH 0/4] cpu: Bulk CPU Hotplug support.

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Message-Id: <20090615232318.74b099a6.akpm@linux-foundation.org>
Date:	Mon, 15 Jun 2009 23:23:18 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Gautham R Shenoy <ego@...ibm.com>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Balbir Singh <balbir@...ibm.com>,
	Rusty Russel <rusty@...tcorp.com.au>,
	Paul E McKenney <paulmck@...ibm.com>,
	Nathan Lynch <ntl@...ox.com>, Ingo Molnar <mingo@...e.hu>,
	Venkatesh Pallipadi <venkatesh.pallipadi@...el.com>,
	Vaidyanathan Srinivasan <svaidy@...ux.vnet.ibm.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Shoahua Li <shaohua.li@...ux.com>
Subject: Re: [RFD PATCH 0/4] cpu: Bulk CPU Hotplug support.

On Tue, 16 Jun 2009 11:08:39 +0530 Gautham R Shenoy <ego@...ibm.com> wrote:

> Currently on a ppc64 box with 16 CPUs, the time taken for
> a individual cpu-hotplug operation is as follows.
> 
> 	# time echo 0 > /sys/devices/system/cpu/cpu2/online
> 	real    0m0.025s
> 	user    0m0.000s
> 	sys     0m0.002s
> 
> 	# time echo 1 > /sys/devices/system/cpu/cpu2/online
> 	real    0m0.021s
> 	user    0m0.000s
> 	sys     0m0.000s

Surprised.  Do people really online and offline CPUs frequently enough
for this to be a problem?

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