linux-kernel - Re: 2.6.19-rc1 genirq causes either boot hang or "do

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Date:	Mon, 09 Oct 2006 09:40:05 +0200
From:	Arjan van de Ven <arjan@...radead.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Linus Torvalds <torvalds@...l.org>,
	Muli Ben-Yehuda <muli@...ibm.com>, Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Rajesh Shah <rajesh.shah@...el.com>, Andi Kleen <ak@....de>,
	"Protasevich, Natalie" <Natalie.Protasevich@...SYS.com>,
	"Luck, Tony" <tony.luck@...el.com>, Andrew Morton <akpm@...l.org>,
	Linux-Kernel <linux-kernel@...r.kernel.org>,
	Badari Pulavarty <pbadari@...il.com>,
	Roland Dreier <rdreier@...co.com>
Subject: Re: 2.6.19-rc1 genirq causes either boot hang or "do_IRQ: cannot
	handle IRQ -1"

> > So yes, having software say "We want to steer this particular interrupt to 
> > this L3 cache domain" sounds eminently sane.
> >
> > Having software specify which L1 cache domain it wants to pollute is 
> > likely just crazy micro-management.
> 
> The current interrupt delivery abstraction in the kernel is a
> set of cpus an interrupt can be delivered to.  Which seem sufficient
> to the cause of aiming at a cache domain.  Frequently the lower
> levels of interrupt delivery map this to a single cpu because of
> hardware limitations but in certain cases we can honor a multiple cpu
> request.
> 
> I believe the scheduler has knowledge about different locality domains
> for NUMA and everything else.  So what is wanting on our side is some
> architecture? work to do the broad steering by default.


well normally this is the job of the userspace IRQ balancer to get
right; the thing is undergoing a redesign right now to be smarter and
deal better with dual/quad core, numa etc etc, but as a principle thing
this is best done in userspace (simply because there's higher level
information there, like "is this interrupt for a network device", so
that policy can take that into account)


-- 
if you want to mail me at work (you don't), use arjan (at) linux.intel.com

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