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Re: performance differences: "maxcpus=1" vs. "echo 0 > /sys/devices/system/cpu/cpu1/online"

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From: Andi Kleen <andi@...>
To: Luciano Rocha <luciano@...>
Cc: Michael Meyer <mike65134@...>, <linux-kernel@...>
Subject: Re: performance differences: "maxcpus=1" vs. "echo 0 &gt; /sys/devices/system/cpu/cpu1/online"
Date: Tuesday, March 25, 2008 - 1:16 pm

Luciano Rocha <luciano@eurotux.com> writes:


CPU hot unplug will do the same. But it is unlikely it accounts
for that much performance difference.

If he used maxcpus=0 it would make sense. maxcpus=0 disables
the IO-APIC which likely makes a large difference. But it should
be actually slower.

There should be actually no difference in theory between max_cpus=1
and hot unplug to one CPU. Might be some bug.

-Andi
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Messages in current thread:
performance differences: "maxcpus=1" vs. "echo 0 &gt; /sys/d..., Michael Meyer, (Tue Mar 25, 9:47 am)
Re: performance differences: "maxcpus=1" vs. "echo 0 &gt; /s..., Bernd Eckenfels, (Sat Mar 29, 7:22 pm)
Re: performance differences: "maxcpus=1" vs. "echo 0 &gt; /s..., Pavel Machek, (Fri Mar 28, 9:59 am)
Re: performance differences: "maxcpus=1" vs. "echo 0 &gt; /s..., Michael Meyer, (Sat Mar 29, 4:55 pm)
Re: performance differences: "maxcpus=1" vs. "echo 0 &gt; /s..., Pavel Machek, (Sat Mar 29, 5:22 pm)
Re: performance differences: "maxcpus=1" vs. "echo 0 &gt; /s..., Michael Meyer, (Sat Mar 29, 6:16 pm)
Re: performance differences: "maxcpus=1" vs. "echo 0 &gt; /s..., Pavel Machek, (Wed Apr 2, 7:31 am)
Re: performance differences: "maxcpus=1" vs. "echo 0 &gt; /s..., Luciano Rocha, (Tue Mar 25, 10:08 am)
Re: performance differences: "maxcpus=1" vs. "echo 0 > /s..., Andi Kleen, (Tue Mar 25, 1:16 pm)
Re: performance differences: "maxcpus=1" vs. "echo 0 &gt; /s..., Pavel Machek, (Fri Mar 28, 10:00 am)
Re: performance differences: "maxcpus=1" vs. "echo 0 &gt; /s..., Michael Meyer, (Tue Mar 25, 1:23 pm)
Re: performance differences: "maxcpus=1" vs. "echo 0 &gt; /s..., Len Brown, (Tue Mar 25, 7:27 pm)
Re: performance differences: "maxcpus=1" vs. "echo 0 &gt; /s..., Michael Meyer, (Wed Mar 26, 3:26 am)
Re: performance differences: "maxcpus=1" vs. "echo 0 &gt; /s..., Wander Winkelhorst, (Tue Mar 25, 1:49 pm)
Re: performance differences: "maxcpus=1" vs. "echo 0 &gt; /s..., Michael Meyer, (Tue Mar 25, 1:56 pm)
Re: performance differences: "maxcpus=1" vs. "echo 0 &gt; /s..., Andi Kleen, (Tue Mar 25, 1:57 pm)
Re: performance differences: "maxcpus=1" vs. "echo 0 &gt; /s..., Michael Meyer, (Tue Mar 25, 12:38 pm)