linux-kernel - Re: Lossy interrupts on x86

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Date:	Wed, 12 Sep 2007 19:06:35 +0200
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Jesse Barnes <jbarnes@...tuousgeek.org>
Cc:	Randy Dunlap <randy.dunlap@...cle.com>,
	linux-kernel@...r.kernel.org
Subject: Re: Lossy interrupts on x86_64

On Wed, 2007-09-12 at 09:29 -0700, Jesse Barnes wrote:
> On Wednesday, September 12, 2007, Randy Dunlap wrote:
> > On Wed, 12 Sep 2007 08:33:15 -0700 Jesse Barnes wrote:
> > > I just narrowed down a weird problem where I was losing more than
> > > 50% of my vblank interrupts to what seems to be the hires timers
> > > patch.  Stock 2.6.23-rc5 works fine, but the latest (171) kernel
> > > from rawhide drops most of my interrupts unless I also have another
> > > interrupt source running (e.g. if I hold down a key or move the
> > > mouse I get the expected number of vblank interrupts, otherwise I
> > > get between 3 and 30 instead of the expected 60 per second).
> > >
> > > Any ideas?  It seems like it might be bad APIC programming, but I
> > > haven't gone through those mods to look for suspects...
> >
> > Also tickless?  (NO_HZ ?)
> >
> > I think I've seen some emails about tickless and keystrokes being
> > needed to cause interrupts... but I'm not postive about it.

That's a suspend / resume problem which we are hunting.

> > but you said "any ideas"
> 
> Yeah, there's NO_HZ in the rawhide kernel too, but I'm getting timer
> ticks normally afaict, it's just vblank interrupts that get lost...

Jesse,

does it make any difference when you boot the box with:

nohz=off

on the kernel command line ?

	tglx


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