linux-kernel - Re: [PATCH v4 5/5] sched: ARM: create a dedicated scheduler topology table

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Date:	Fri, 25 Apr 2014 18:05:53 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Vincent Guittot <vincent.guittot@...aro.org>
Cc:	Dietmar Eggemann <dietmar.eggemann@....com>,
	"mingo@...nel.org" <mingo@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"tony.luck@...el.com" <tony.luck@...el.com>,
	"fenghua.yu@...el.com" <fenghua.yu@...el.com>,
	"schwidefsky@...ibm.com" <schwidefsky@...ibm.com>,
	"cmetcalf@...era.com" <cmetcalf@...era.com>,
	"benh@...nel.crashing.org" <benh@...nel.crashing.org>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"preeti@...ux.vnet.ibm.com" <preeti@...ux.vnet.ibm.com>,
	"linaro-kernel@...ts.linaro.org" <linaro-kernel@...ts.linaro.org>
Subject: Re: [PATCH v4 5/5] sched: ARM: create a dedicated scheduler topology
 table

On Fri, Apr 25, 2014 at 06:04:19PM +0200, Peter Zijlstra wrote:
> > The example above is consistent because CPU2 mask and CPU0 mask are
> > fully exclusive
> > 
> > so
> > CPU0: cpu_corepower_mask=0-1
> > CPU2: cpu_corepower_mask=2
> > are consistent
> > 
> > CPU0: cpu_corepower_mask=0-2
> > CPU2: cpu_corepower_mask=0-2
> > are also consistent
> > 
> > but
> > 
> > CPU0: cpu_corepower_mask=0-1
> > CPU2: cpu_corepower_mask=0-2
> > are not consistent
> > 
> > and your example uses the last configuration
> > 
> > To be more precise, the rule above applies on default SDT definition
> > but the flag SD_OVERLAP enables such kind of overlap between group.
> > Have you tried it ?
> 
> I've never tried degenerate stuff with SD_OVERLAP, it might horribly
> explode -- its not actually meant to work.
> 
> The SD_OVERLAP comes from not fully connected NUMA topologies; suppose
> something like:
> 
>         0------1
>         |      |
>         |      |
>         2------3
> 
> or:
> 
>  ( 10 20 20  0 )
>  ( 20 10  0 20 )
>  ( 20  0 10 20 )
>  (  0 20 20 10 )

d'0h: s/0/30/

0 <-> 3 is 2 hops, too focused on the single hop case

> Your domain level that models the single-hop/20 distance has overlapping
> masks:
> 
> N0: 0-2
> N1: 0,1,3
> N2: 0,2,3
> N3: 1-3
> 
> I've never tried to construct a NUMA topology that would be overlapping
> and have redundant bits in.
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