linux-kernel - Re: [PATCH 3/3] x86: fix node_possible

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Message-ID: <20090511222608.61b99dad@lxorguk.ukuu.org.uk>
Date:	Mon, 11 May 2009 22:26:08 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	David Rientjes <rientjes@...gle.com>,
	Jack Steiner <steiner@....com>,
	Yinghai Lu <yinghai@...nel.org>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] x86: fix node_possible_map logic -v2

> CPU [0-1] cannot be considered local in either node, since they are 
> further away from the memory than either, and furthermore, unlike either 
> of the memory nodes, they have no preference for memory from either of 
> the other two nodes (quite on the contrary; they would probably benefit 
> from drawing from both.)

Surely you should schedule based on the memory bandwidth at that point ?
Assuming the data collection overhead is acceptable. A long time ago
someone did a paper on a related topic (Scheduling by memory bandwidth on
the grounds that memory not CPU bandwidth was the resource most
constrained) and that demonstrated that for quite a few processors the
memory bandwidth data is cheaply available in the profiling registers.

Alan
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