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From: David Miller <davem@davemloft.net>
Subject: Re: [PATCH] INET : removes per bucket rwlock in tcp/dccp ehash
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Date: Sun, 04 Nov 2007 13:56:21 -0800 (PST)
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From: Andi Kleen <ak@suse.de>
Date: Sun, 4 Nov 2007 13:26:38 +0100

> 
> > But I suspect distributions kernels enable CONFIG_HOTPLUG_CPU so 
> > num_possible_cpus() will be NR_CPUS.
> 
> Nope, on x86 num_possible_cpus() is derived from BIOS tables these days.

And similarly on SPARC64 is will be set based upon the
physical capabilities of the system.

This makes a huge different as we have to set NR_CPUS to 4096
in order to handle the cpu numbering of some UltraSPARC-IV
machines.