linux-kernel - Re: getting processor numbers

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Message-ID: <20070403173505.GD23689@one.firstfloor.org>
Date:	Tue, 3 Apr 2007 19:35:05 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Ulrich Drepper <drepper@...hat.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Linux Kernel <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: getting processor numbers

On Tue, Apr 03, 2007 at 10:30:47AM -0700, Ulrich Drepper wrote:
> Andi Kleen wrote:
> > Topology is dependent on the number of CPUs.
> 
> Not all of it.

What is not?

>  We might add very limited caching (for a few
> seconds) but that's as much as we can go.

Hmm, e.g. in OpenMP you would have another thread that just reads /proc/cpuinfo
in a loop and starts new threads on new CPUs?

That sounds ...... "expensive" 

The other use case in glibc I know of is the Opteron optimized
memcpy which can use different functions depending on the number of
cores.  But having a separate thread regularly rereading cpuinfo for
memcpy also sounds quite crazy.

-Andi
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