linux-kernel - Re: [patch 6/6] x86: cpumask_of_node() should handle -1 as a node

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Date:	Thu, 7 Jan 2010 10:31:51 +1100
From:	Anton Blanchard <anton@...ba.org>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [patch 6/6] x86: cpumask_of_node() should handle -1 as a node


Hi David,

> Do we really want to do this?  A nid of -1 is undefined, so the result of 
> cpumask_of_node(-1) should be undefined; there's no formal definition that 
> a nid of -1 follows the semantics that we use for x86 pci buses, for 
> example, where it implies no NUMA locality in all cases.

I don't like the use of -1 as a node, but it's much more widespread than
x86; including sh, powerpc, sparc and the generic topology code. eg:


#fdef CONFIG_PCI
extern int pcibus_to_node(struct pci_bus *pbus);
#else
static inline int pcibus_to_node(struct pci_bus *pbus)
{
        return -1;
}


It would be nice to get rid of this special case but I suspect that's not
2.6.33 material.

Speaking of invalid node ids, I also noticed the scheduler isn't using
node iterators:

        for (i = 0; i < nr_node_ids; i++) {

which should be fixed at some stage too since it doesn't allow us to
allocate the node structures sparsely.

Anton
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