linux-kernel - Re: [PATCH] sched/topology: Use Identity node only if required

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Message-ID: <20180829085738.GS24142@hirez.programming.kicks-ass.net>
Date:   Wed, 29 Aug 2018 10:57:38 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:     Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Rik van Riel <riel@...riel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Michael Ellerman <mpe@...erman.id.au>,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
        linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>,
        Andre Wild <wild@...ux.vnet.ibm.com>
Subject: Re: [PATCH] sched/topology: Use Identity node only if required

On Wed, Aug 29, 2018 at 10:43:48AM +0200, Peter Zijlstra wrote:
> DIE(j) should be:
> 
> 	cpu_cpu_mask(j) := cpumask_of_node(cpu_to_node(j))

FWIW, I was expecting that to be topology_core_cpumask(), so I'm a
little confused myself just now.

> and NODE(j) should be:
> 
> 	\Union_k cpumask_of_node(k) ; where node_distance(j,k) <= node_distance(0,0)
> 
> which, _should_ reduce to:
> 
> 	cpumask_of_node(j)
> 
> and thus DIE and NODE _should_ be the same here.
> 
> So what's going sideways?