Message-ID: <4A42C131.6040007@zytor.com>
Date: Wed, 24 Jun 2009 17:13:37 -0700
From: "H. Peter Anvin" <hpa@zytor.com>
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To: Andi Kleen <andi@firstfloor.org>
CC: Andrew Morton <akpm@linux-foundation.org>, Tejun Heo <tj@kernel.org>,
       linux-kernel@vger.kernel.org, x86@kernel.org,
       linux-arch@vger.kernel.org, mingo@elte.hu, tglx@linutronix.de,
       cl@linux-foundation.org
Subject: Re: [PATCHSET] percpu: generalize first chunk allocators and improve
 lpage NUMA support
References: <1245850216-31653-1-git-send-email-tj@kernel.org> <20090624165508.30b88343.akpm@linux-foundation.org> <20090625000202.GR6760@one.firstfloor.org>
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Andi Kleen wrote:
> 
> Haven't read the new patches, but per cpu data always was sized
> for all possible CPUs.
> 
>> and N is large, what did it cost?
> 
>> And what are reasonable values of N?
> 
> N should normally not be large anymore, since num_possible_cpus() 
> is sized based on firmware information now.
> 

*Ahem* virtual machines *ahem*...

I have discussed this with Tejun, and the plan is to allocate the percpu
information when a processor is first brought online (but not removed
when it is offlined again.)  It's a real problem for 32-bit VMs, so it's
more important than you'd think.

	-hpa

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