linux-kernel - Re: [PATCH] mm, x86: Skip NUMA_NO

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Date:	Thu, 5 Dec 2013 15:21:00 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
cc:	Toshi Kani <toshi.kani@...com>, akpm@...ux-foundation.org,
	mingo@...nel.org, hpa@...or.com, tglx@...utronix.de,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org, x86@...nel.org
Subject: Re: [PATCH] mm, x86: Skip NUMA_NO_NODE while parsing SLIT

On Thu, 5 Dec 2013, Yasuaki Ishimatsu wrote:

> (2013/12/05 6:09), Toshi Kani wrote:
> > When ACPI SLIT table has an I/O locality (i.e. a locality unique
> > to an I/O device), numa_set_distance() emits the warning message
> > below.
> > 
> >   NUMA: Warning: node ids are out of bound, from=-1 to=-1 distance=10
> > 
> > acpi_numa_slit_init() calls numa_set_distance() with pxm_to_node(),
> > which assumes that all localities have been parsed with SRAT previously.
> > SRAT does not list I/O localities, where as SLIT lists all localities
> 
> > including I/Os.  Hence, pxm_to_node() returns NUMA_NO_NODE (-1) for
> > an I/O locality.  I/O localities are not supported and are ignored
> > today, but emitting such warning message leads unnecessary confusion.
> 
> In this case, the warning message should not be shown. But if SLIT table
> is really broken, the message should be shown. Your patch seems to not care
> for second case.
> 

It's a subtle problem of the difference in the definition of a "NUMA node" 
between the ACPI specification and how it is defined in the kernel.  The 
specification allows I/O buses to define a NUMA node and the kernel 
doesn't setup a separate node id for them, so there's no way to 
distinguish between an erroneous SLIT and system localities that only 
include I/O devices.  If that were to change in the future we could remove 
this limitation since pxm_to_node() wouldn't return NUMA_NO_NODE for 
Toshi's config.  A follow-up patch that adds the comment about why this is 
done has been proposed to be folded into this patch.
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