From: Andi Kleen <ak@muc.de>
To: Andrew Morton <akpm@osdl.org>
Subject: Re: [PATCH] percpu data: only iterate over possible CPUs
Date: Fri, 10 Feb 2006 13:10:58 +0100
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On Friday 10 February 2006 11:42, Andrew Morton wrote:
> Andi Kleen <ak@muc.de> wrote:
> >
> > On Thursday 09 February 2006 19:04, Andrew Morton wrote:
> > > Ashok Raj <ashok.raj@intel.com> wrote:
> > > >
> > > > The problem was with ACPI just simply looking at the namespace doesnt
> > > >  exactly give us an idea of how many processors are possible in this platform.
> > > 
> > > We need to fix this asap - the performance penalty for HOTPLUG_CPU=y,
> > > NR_CPUS=lots will be appreciable.
> > 
> > What is this performance penalty exactly? 
> 
> All those for_each_cpu() loops will hit NR_CPUS cachelines instead of
> hweight(cpu_possible_map) cachelines.

But are there any in real fast paths? iirc they are mostly in initialization,
where it doesn't matter too much.

-Andi
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