linux-kernel - Re: Linux 2.6.39-rc3

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Date:	Sun, 17 Apr 2011 21:12:47 -0400
From:	Jerome Glisse <j.glisse@...il.com>
To:	Joerg Roedel <joro@...tes.org>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	Tejun Heo <tj@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Yinghai Lu <yinghai@...nel.org>, alexandre.f.demers@...il.com
Subject: Re: Linux 2.6.39-rc3

On Sun, Apr 17, 2011 at 10:09 AM, Joerg Roedel <joro@...tes.org> wrote:
> On Sat, Apr 16, 2011 at 02:54:04PM -0400, Jerome Glisse wrote:
>
>> If you want to go the printk way you can add printk before each test
>> ring_test, ib_test in r600.c this 2 functions are the own that might
>> trigger the first GPU gart activities.
>
> Okay, I found the place in source that triggers this. It happens in the
> function r600_ib_test. The interesting thing is that not the ib-command
> itself is responsible but the fence that is emitted afterwards (proved
> by removing the fence command, where the problem went away).
> I don't know enough about the command semantics to make a guess what
> goes wrong there. But maybe you GPU folks have an idea?
>
>        Joerg
>
>

I can't think of any theory, at that point the wb, irq ring, cp buffer
& ib pool are all allocated and pinned into gtt so they all have valid
entry backed by a real page. Maybe the GART flush & update is
seriously buggy but i expect we would have been hurt sooner by such
things. Maybe there is a bug in the hw... wouldn't be surprised. Will
try to think to crazy theory.

Cheers,
Jerome
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