linux-kernel - Re: performance differences: "maxcpus=1" vs. "echo 0

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Message-ID: <22851.90444.qm@web25806.mail.ukl.yahoo.com>
Date:	Tue, 25 Mar 2008 17:38:15 +0100 (CET)
From:	Michael Meyer <mike65134@...oo.de>
To:	linux-kernel@...r.kernel.org
Subject: Re: performance differences: "maxcpus=1" vs. "echo 0 > /sys/devices/system/cpu/cpu1/online"


--- Luciano Rocha <luciano@...otux.com> schrieb:

> 
> On Tue, Mar 25, 2008 at 02:47:50PM +0100, Michael
> Meyer wrote:
> > Hi, 
> > 
> > what is the difference between booting a dual core
> > machine with "maxcpus=1" or by deactivating the
> second
> > core at run time with "echo 0 >
> > /sys/devices/system/cpu/cpu1/online"?
> 
> maxcpus=1 should turn off the SMP alternative and
> switch to UP only,
> optimising some locks and instructions.

Can this be achieved during runtime also? And is it
possible to switch back to SMP after that?


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