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Subject: Re: 2.6.21-rc1: known regressions (v2) (part 2)
From: Thomas Gleixner <tglx@linutronix.de>
Reply-To: tglx@linutronix.de
To: Con Kolivas <kernel@kolivas.org>
Cc: Ingo Molnar <mingo@elte.hu>, Mike Galbraith <efault@gmx.de>,
       Michal Piotrowski <michal.k.k.piotrowski@gmail.com>,
       Adrian Bunk <bunk@stusta.de>,
       Linus Torvalds <torvalds@linux-foundation.org>,
       Andrew Morton <akpm@linux-foundation.org>, linux-kernel@vger.kernel.org
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Date: Thu, 01 Mar 2007 12:33:56 +0100
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On Thu, 2007-03-01 at 22:13 +1100, Con Kolivas wrote:
> > if then there should be a mechanism /in the hardware/ to set the
> > priority of a CPU - and then the hardware could decide how to prioritize
> > between siblings. Doing this in software is really hard.
> 
> And that's the depressing part because of course I was interested in that as 
> the original approach to the problem (and it was a big problem). When I spoke 
> to Intel and AMD (of course to date no SMT AMD chip exists) at kernel summit 
> they said it was too hard to implement hardware priorities well. Which is 
> real odd since IBM have already done it with Power...
> 
> Still I think it has been working fine in software till now, but now it has to 
> deal with the added confusion of dynticks, so I already know what will happen 
> to it.

Well, it's not a dyntick problem in the first place. Even w/o dynticks
we go idle with local_softirq_pending(). Dynticks contains an explicit
check for that, which makes it visible.

	tglx