linux-kernel - Re: [PATCH 15/15] x86: Fix cpu_coregroup_mask to return correct cpumask on multi-node processors

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Message-Id: <1251196502.7538.1136.camel@twins>
Date:	Tue, 25 Aug 2009 12:35:02 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andreas Herrmann <andreas.herrmann3@....com>
Cc:	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 15/15] x86: Fix cpu_coregroup_mask to return correct
 cpumask on multi-node processors

On Tue, 2009-08-25 at 12:24 +0200, Andreas Herrmann wrote:
> On Tue, Aug 25, 2009 at 11:55:43AM +0200, Peter Zijlstra wrote:
> > On Tue, 2009-08-25 at 11:31 +0200, Andreas Herrmann wrote:
> > > On Mon, Aug 24, 2009 at 05:36:16PM +0200, Peter Zijlstra wrote:
> > > > On Thu, 2009-08-20 at 15:46 +0200, Andreas Herrmann wrote:
> > > > > The correct mask that describes core-siblings of an processor
> > > > > is topology_core_cpumask. See topology adapation patches, especially
> > > > > http://marc.info/?l=linux-kernel&m=124964999608179
> > > > 
> > > > 
> > > > argh, violence, murder kill.. this is the worst possible hack and you're
> > > > extending it :/
> > > 
> > > So this is the third code area
> > > (besides sched_*_power_savings sysfs interface, and the __cpu_power fiddling)
> > > that is crap, mess, a hack.
> > > 
> > > Didn't know that I'd enter such a minefield when touching this code. ;-(
> > 
> > Yeah, you're lucky that way ;-) Its been creaking for a while, and I've
> > been making noises to the IBM people (who so far have been the main
> > source of power saving patches) to clean this up, but now you trod onto
> > all of it at once..
> > 
> > > What would be your perferred solution for the
> > > core_cpumask/llc_shared_map stuff?  Another domain level to get rid of
> > > this function?
> > 
> > Right, I'd like to see everything exposed as domain levels.
> > 
> > 
> > numa-cluster
> > numa
> > socket
> > in-socket-numa
> > multi-core
> > shared-cache
> > core
> > threads
> > 
> > We currently have a fixed order of these things, but I think we should
> > simply provide helpers for building the sd tree and let the arch code do
> > that instead of exporting all these masks in a fixed order.
> > 
> > Once we get the arch domain tree, we do degenerate stuff to cull all the
> > trivial domains and fold SD flags.
> 
> So any in-socket-numa is only going to haeppen with the arch-defined
> domain tree.

Well, we could see what it takes to make this work without that. I mean,
this is just how I'd like to see it end up, doesn't mean we cannot work
on it from multiple angles at the same time.

> Now that this is settled you should throw away the
> __build_sched_domains cleanup patches that are in tip. They won't be
> of use when domain creation code is basically changed.

I'm not sure that's needed, we can continue work on refactoring that.
Small steps towards something better seems a better plan than a single
large step.


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