linux-kernel - Re: [REGRESSION, i915]: Periodic stalls with 2.6.36-rc2

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Date:	Tue, 24 Aug 2010 10:00:47 +0100
From:	Chris Wilson <chris@...is-wilson.co.uk>
To:	Sitsofe Wheeler <sitsofe@...oo.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	dri-devel@...ts.freedesktop.org
Subject: Re: [REGRESSION, i915]: Periodic stalls with 2.6.36-rc2

On Tue, 24 Aug 2010 09:49:02 +0100, Sitsofe Wheeler <sitsofe@...oo.com> wrote:
> On Tue, Aug 24, 2010 at 09:16:50AM +0100, Chris Wilson wrote:
> > 
> > Ok, I'm a little happier that the hangcheck could be just another symptom
> > of the problem...
> > 
> > I think it is safe to assume that the bug is in i915, so restricting the
> > bisect to just drm seems plausible:
> > 
> > git bisect start drivers/gpu/drm
> > git bisect good 2.6.36-rc1
> > git bisect bad 2.6.36-rc2
> 
> I should mention that I ran a similar bisect yesterday but it led to a dead
> end:
[snip]
> All the bad kernels above boot EXTREMELY slowly and it's not clear why. Using
> the results above to run your tests produced the following:

I was hoping that git would be more intelligent than that. Is there a way
to simply bisect down one side of a merge?

The slow boot is probably fixed by 4936a3b90d79dd8775c6ac23c2cf2dcebe29abde.
A trivial patch you can apply on each step is:

diff --git a/arch/x86/kernel/hpet.c b/arch/x86/kernel/hpet.c
index 33dbcc4..88f3b6c 100644
--- a/arch/x86/kernel/hpet.c
+++ b/arch/x86/kernel/hpet.c
@@ -837,7 +837,7 @@ static int hpet_clocksource_register(void)
         * cyc/sec = FSEC_PER_SEC/hpet_period(fsec/cyc)
         * cyc/sec = (FSEC_PER_NSEC * NSEC_PER_SEC)/hpet_period
         */
-       hpet_freq = FSEC_PER_NSEC * NSEC_PER_SEC;
+       hpet_freq = (u64) FSEC_PER_NSEC * NSEC_PER_SEC;
        do_div(hpet_freq, hpet_period);
        clocksource_register_hz(&clocksource_hpet, (u32)hpet_freq);

-- 
Chris Wilson, Intel Open Source Technology Centre
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