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

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Message-ID: <16336.23884.qm@web25814.mail.ukl.yahoo.com>
Date:	Tue, 25 Mar 2008 14:47:50 +0100 (CET)
From:	Michael Meyer <mike65134@...oo.de>
To:	linux-kernel@...r.kernel.org
Subject: performance differences: "maxcpus=1" vs. "echo 0 > /sys/devices/system/cpu/cpu1/online"

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"?

I observed a funny behaviour of apache ant: although
it uses javac which is single threaded, a compile run
with "maxcpus=1" is actually faster than a compile run
with both cores activated. But with the second core
deactivated using "echo 0 >
/sys/devices/system/cpu/cpu1/online" it is even slower
than with both cores.

Is here any method to get the exact same behaviour of
"maxcpus=1" with disabling the second core only
temporarily? So that the second core could be disabled
before the ant execution and enabled after the ant
execution?

Thanks a lot!

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