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

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Date:	Mon, 13 Jun 2016 15:19:42 +0200
From:	Martin Schwidefsky <schwidefsky@...ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Heiko Carstens <heiko.carstens@...ibm.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] s390/topology: add drawer scheduling domain level

On Mon, 13 Jun 2016 15:06:47 +0200
Peter Zijlstra <peterz@...radead.org> wrote:

> On Mon, Jun 13, 2016 at 01:22:30PM +0200, Heiko Carstens wrote:
> > Yes, and actually we are all virt/LPAR always, so this is unfortunately not
> > very easy to do. And yes, I do agree that for the 1:1 case it most likely
> > would make sense, however we don't have any run-time guarantee to stay 1:1.
> 
> One option would be to make it a boot option; such that the
> administrator has to set it. At that point, if the admin creates
> multiple LPARs its on him.

Unfortunately not good enough. The LPAR code tries to optimize the layout
at the time a partition is activated. The landscape of already running
partitions can change at this point.

To get around this you would have to activate *all* partitions first and
then start the operating systems in a second step.

And then there is concurrent repair which will move things around if a
piece of memory goes bad. This happens rarely though.

-- 
blue skies,
   Martin.

"Reality continues to ruin my life." - Calvin.