linux-kernel - Re: [PATCH 2/2] s390/topology: add drawer scheduling domain level

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Message-ID: <20160613110621.GV30909@twins.programming.kicks-ass.net>
Date:	Mon, 13 Jun 2016 13:06:21 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Heiko Carstens <heiko.carstens@...ibm.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] s390/topology: add drawer scheduling domain level

On Wed, Jun 08, 2016 at 11:09:16AM +0200, Heiko Carstens wrote:
> The z13 machine added a fourth level to the cpu topology
> information. The new top level is called drawer.
> 
> A drawer contains two books, which used to be the top level.
> 
> Adding this additional scheduling domain did show performance
> improvements for some workloads of up to 8%, while there don't
> seem to be any workloads impacted in a negative way.

Right; so no objection.

Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>

You still don't want to make NUMA explicit on this thing? So while I
suppose the SC 480M L4 cache does hide some of it, there can be up to 8
nodes on this thing. Which seems to me there's win to be had by exposing
it.

Of course, the moment you go all virt/LPAR on it, that all gets really
interesting, but for those cases where you run 1:1 it might make sense.

Also, are you sure you don't want some of the behaviour changed for the
drawer domains? I could for example imagine you wouldn't want
SD_WAKE_AFFINE set (we disable that for NUMA domains as well).