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

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Date:	Fri, 25 Apr 2014 18:04:19 +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

> 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 )

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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