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Subject: Re: isolcpus weirdness
From: Emmanuel Pacaud <emmanuel.pacaud@univ-poitiers.fr>
To: Nick Piggin <nickpiggin@yahoo.com.au>
Cc: linux-kernel@vger.kernel.org
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Date: Thu, 23 Feb 2006 14:07:33 +0100
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Le jeudi 23 février 2006 à 23:21 +1100, Nick Piggin a écrit :
> Emmanuel Pacaud wrote:
> > Hi,
> > 
> > When specifying isolcpus kernel parameters, isolated cpu is always the
> > same, not the one I asked for.
..
> > 
> > What's wrong ?
> > 
> 
> If you have 2 CPUs, and "isolate" one of them, the other is isolated
> from it. Ie. there is no difference between isolating one or the other,
> the net result is that they are isolated from each other.
> 

>From kernel-parameters.txt:

+   isolcpus=   [KNL,SMP] Isolate CPUs from the general scheduler.
+         Format: <cpu number>, ..., <cpu number>
+         This option can be used to specify one or more CPUs
+         to isolate from the general SMP balancing and scheduling
+         algorithms. The only way to move a process onto or off
+         an "isolated" CPU is via the CPU affinity syscalls.
+
+         This option is the preferred way to isolate CPUs. The
+         alternative - manually setting the CPU mask of all tasks
+         in the system can cause problems and suboptimal load
+         balancer performance.

There's a difference between isolated cpus and other cpus: by default,
there's almost no activity on isolated ones. That's what I want to be
able to do.

	Emmanuel.

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