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

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Message-ID: <19D0D50E9B1D0A40A9F0323DBFA04ACC023B0D18@USRV-EXCH4.na.uis.unisys.com>
Date:	Mon, 9 Oct 2006 11:02:45 -0500
From:	"Protasevich, Natalie" <Natalie.Protasevich@...SYS.com>
To:	"Arjan van de Ven" <arjan@...radead.org>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	"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>,
	"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: cannothandle IRQ -1"

> On Mon, 2006-10-09 at 10:28 -0500, Protasevich, Natalie wrote:
> 
> > I'd like also to question current policies of user space 
> irqbalanced. 
> > It seems to just go round-robin without much heuristics involved.
> 
> only for the timer interrupt and only because "people" didn't 
> want to see it bound to a specific CPU. For all others 
> there's quite some heuristics actually

Ah, this explains a lot. I was planning to try binding the timer to a
CPU or a node (as soon as get a system for testing).

> 
> >  We are
> > seeing loss of timer interrupts on our systems - and the more 
> > processors the more noticeable it is, but it starts even on 8x 
> > partitions; on 48x system I see about 50% loss, on both ia32 and 
> > x86_64 (haven't checked on
> > ia64 yet). With say 16 threads it is unsettling to see 70% overall 
> > idle time, and still only 40-50% of interrupts go through. System's 
> > time is not affected, so the problem is on the back burner 
> for now :) 
> > It's not clear yet whether this is software or hardware fault,
> 
> I'd call it a hardware fault. But them I'm biased.

It is the main suspect for now, yes (I tend to be biased this way too :)
Those are NUMA machines that run as non-NUMA sometimes, and I still need
to sort out if it happens in both cases, or either and all the aspects
that may have come into play.  
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