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Subject: Re: sched: fix/optimise some issues
From: Peter Zijlstra <peterz@infradead.org>
To: Stephan =?ISO-8859-1?Q?B=E4rwolf?= 
	<stephan.baerwolf@tu-ilmenau.de>
Cc: linux-kernel@vger.kernel.org, Nikhil Rao <ncrao@google.com>,
        Ingo Molnar <mingo@elte.hu>
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Date: Thu, 21 Jul 2011 18:51:48 +0200
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On Thu, 2011-07-21 at 18:36 +0200, Stephan Bärwolf wrote:
> I also remember weak Linus had sth. against "priority inheritance"
> (don't ask me what or why - I don't know),
> but it would be an honour to me working with you guys to implement
> this feature in future kernels. 

Look at kernel/rt_mutex.c, it as a complete tradition Priority
Inheritance implementation :-)

The trouble is that it only works for SCHED_FIFO/RR.

Now you can extend PI to cover weighted fair queueing, or implement the
much simpler proxy execution policy which generalizes to pretty much any
scheduling algorithm, see for example the paper: "Timeslice donation in
component-based systems" in:

http://www.artist-embedded.org/docs/Events/2010/OSPERT/OSPERT2010-Proceedings.pdf

Extending that to SMP is the 'interesting' bit..

However that will not solve the true idle thing since some
synchronization primitives we have are fundamentally incompatible with
any form of PI (including the various ceiling protocols) :-/, see for
example the traditional semaphore and completions.