linux-kernel - Re: [RFC] bitmap relative operator for mempolicy extensions

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Message-Id: <200802142130.06155.ak@suse.de>
Date:	Thu, 14 Feb 2008 21:30:05 +0100
From:	Andi Kleen <ak@...e.de>
To:	Mike Travis <travis@....com>
Cc:	Christoph Lameter <clameter@....com>, Paul Jackson <pj@....com>,
	David Rientjes <rientjes@...gle.com>, Lee.Schermerhorn@...com,
	mel@....ul.ie, linux-kernel@...r.kernel.org,
	akpm@...ux-foundation.org
Subject: Re: [RFC] bitmap relative operator for mempolicy extensions

On Thursday 14 February 2008 21:25:59 Mike Travis wrote:
> Christoph Lameter wrote:
> > On Thu, 14 Feb 2008, Andi Kleen wrote:
> > 
> >> You're saying the kernel should use these relative masks internally?
> > 
> > There is just some thoughts about this. Did not have time to look into the 
> > details. Mike?
> 
> There are a few places where the entire cpumask is not needed.  For
> example, in the area of core siblings on a node.  There's a limit
> to how many cores/threads can be on a node and the full 4k cpumask
> is not needed.  How this pertains to this new functionality I'm
> not sure yet.

That would require that the BIOS enumerates the CPUs in a way that
the cores of a socket are continuous. While that's usually true
I don't think there's a guarantee. In theory they could be all scattered.

Ok I theory Linux could remap later but that seems hardly worth 
the trouble.

I would rather just use arrays of integers in this case with a reasonable fixed 
upper limit (e.g. 16 or 32 -- if there are ever >32 thread x86 CPUs presumably they will
require an updated cpufreq driver too...) 


-Andi

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