linux-kernel - Re: [tip:sched/core] sched/numa: Rewrite the CONFIG

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Date:	Wed, 06 Jun 2012 11:15:05 +0200
From:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
To:	Alex Shi <lkml.alex@...il.com>
Cc:	mingo@...nel.org, torvalds@...ux-foundation.org,
	cmetcalf@...era.com, tony.luck@...el.com, sivanich@....com,
	akpm@...ux-foundation.org, ralf@...ux-mips.org,
	greg.pearson@...com, ink@...assic.park.msu.ru, tglx@...utronix.de,
	rth@...ddle.net, kamezawa.hiroyu@...fujitsu.com, paulus@...ba.org,
	linux-kernel@...r.kernel.org, hpa@...or.com, anton@...ba.org,
	lethal@...ux-sh.org, davem@...emloft.net, benh@...nel.crashing.org,
	dhowells@...hat.com, mattst88@...il.com, fenghua.yu@...el.com,
	Alex Shi <alex.shi@...el.com>,
	linux-tip-commits@...r.kernel.org
Subject: Re: [tip:sched/core] sched/numa: Rewrite the CONFIG_NUMA sched
 domain support

On Wed, 2012-06-06 at 15:43 +0800, Alex Shi wrote:
> > +       /*
> > +        * O(nr_nodes^2) deduplicating selection sort -- in order to find the
> > +        * unique distances in the node_distance() table.
> > +        *
> > +        * Assumes node_distance(0,j) includes all distances in
> > +        * node_distance(i,j) in order to avoid cubic time.
> 
> Curious for other platforms node_distance number, actually, this
> assumption is right for what I saw Intel platforms. but it is not
> match acpispec50.pdf:
> 
> Table 6-152 Example Relative Distances Between Proximity Domains
> Proximity Domain 0 1 2 3
> 0 10 15 20 18
> 1 15 10 16 24
> 2 20 16 10 12
> 3 18 24 12 10

Yes I know its allowed, I just haven't seen it in practice.

I've got a patch that validates this assumption if you boot with
"sched_debug". If we ever run into such a setup we might need to fix
this -- it shouldn't be too hard, just expensive.
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