Date: Mon, 28 Jan 2008 13:06:37 -0600
From: Paul Jackson <pj@sgi.com>
To: Max Krasnyanskiy <maxk@qualcomm.com>
Cc: a.p.zijlstra@chello.nl, linux-kernel@vger.kernel.org, mingo@elte.hu,
       srostedt@redhat.com, ghaskins@novell.com
Subject: Re: [CPUISOL] CPU isolation extensions
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Max wrote:
> So far it seems that extending cpu_isolated_map
> is more natural way of propagating this notion to the rest of the kernel.
> Since it's very similar to the cpu_online_map concept and it's easy to integrated
> with the code that already uses it. 

If it were just realtime support, then I suspect I'd agree that
extending cpu_isolated_map makes more sense.

But some people use realtime on systems that are also heavily
managed using cpusets.  The two have to work together.  I have
customers with systems running realtime on a few CPUs, at the
same time that they have a large batch scheduler (which is layered
on top of cpusets) managing jobs on a few hundred other CPUs.
Hence with the cpuset 'sched_load_balance' flag I think I've already
done what I think is one part of what your patches achieve by extending
the cpu_isolated_map.

This is a common situation with "resource management" mechanisms such
as cpusets (and more recently cgroups and the subsystem modules it
supports.)  They cut across existing core kernel code that manages such
key resources as CPUs and memory.  As best we can, they have to work
with each other.

-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@sgi.com> 1.940.382.4214
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