linux-kernel - Re: 2.6.21-rc1: known regressions (v2) (part 2)

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Message-Id: <1172748837.11473.53.camel@localhost.localdomain>
Date:	Thu, 01 Mar 2007 12:33:56 +0100
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Con Kolivas <kernel@...ivas.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Mike Galbraith <efault@....de>,
	Michal Piotrowski <michal.k.k.piotrowski@...il.com>,
	Adrian Bunk <bunk@...sta.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: 2.6.21-rc1: known regressions (v2) (part 2)

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


	

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