linux-kernel - Re: [BUG] IO-APIC + timer doesn't work!

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Message-ID: <20090418200623.GA27294@elte.hu>
Date:	Sat, 18 Apr 2009 22:06:23 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Jeff Mahoney <jeffm@...e.com>
Cc:	Jan Kiszka <jan.kiszka@....de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andreas Herrmann <andreas.herrmann3@....com>
Subject: Re: [BUG] IO-APIC + timer doesn't work!


* Jeff Mahoney <jeffm@...e.com> wrote:

> > Hmmmmm. That somehow reminds me of what I thought I had to fix in the
> > HPET emulation of QEMU just recently [1] - because of 2.6.30-rc's behavior.
> > 
> > Could you try if writing 'delta' a second time makes any difference on
> > that box?
> > 
> > diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
> > index 648b3a2..523d72b 100644
> > --- a/arch/x86/kernel/hpet.c
> > +++ b/arch/x86/kernel/hpet.c
> > @@ -324,6 +324,7 @@ static void hpet_set_mode(enum clock_event_mode mode,
> >  		       HPET_TN_SETVAL | HPET_TN_32BIT;
> >  		hpet_writel(cfg, HPET_Tn_CFG(timer));
> >  		hpet_writel((unsigned long) delta, HPET_Tn_CMP(timer));
> > +		hpet_writel((unsigned long) delta, HPET_Tn_CMP(timer));
> >  		hpet_start_counter();
> >  		hpet_print_config();
> >  		break;
> > 
> 
> Thanks, Jan.
> 
> That fixed it for me.

I've queued it up (and i've got a test-system that might be affected 
by a similar problem - it shows a similar crash very rarely), but it 
would be nice to know why this duplicate writeout makes a 
difference. Jan?

	Ingo
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