linux-kernel - Re: [PATCHSET] percpu: generalize first chunk allocators and improve lpage NUMA support

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Date:	Thu, 25 Jun 2009 02:02:02 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org,
	x86@...nel.org, linux-arch@...r.kernel.org, mingo@...e.hu,
	andi@...stfloor.org, hpa@...or.com, tglx@...utronix.de,
	cl@...ux-foundation.org
Subject: Re: [PATCHSET] percpu: generalize first chunk allocators and improve lpage NUMA support

> I assume from the tremendous number of for_each_possible_cpu()s that
> CPU hotplug awareness won't be happening.
> 
> Do we have a feeling for the amount of wastage here?  If
> 
> 	num_possible_cpus() - num_online_cpus() == N

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.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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