linux-kernel - Re: [Nouveau] [PATCH 09/17] drm/radeon: use common fence implementation for fences

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Message-ID: <CAKMK7uHVh+gUXzQ+eYeV5rzHDxbkZ_9E3C7_m6=VOUzXRpALXQ@mail.gmail.com>
Date:	Wed, 23 Jul 2014 10:01:56 +0200
From:	Daniel Vetter <daniel.vetter@...ll.ch>
To:	Christian König <christian.koenig@....com>
Cc:	Christian König <deathsimple@...afone.de>,
	Maarten Lankhorst <maarten.lankhorst@...onical.com>,
	Thomas Hellstrom <thellstrom@...are.com>,
	nouveau <nouveau@...ts.freedesktop.org>,
	LKML <linux-kernel@...r.kernel.org>,
	dri-devel <dri-devel@...ts.freedesktop.org>,
	Ben Skeggs <bskeggs@...hat.com>,
	"Deucher, Alexander" <alexander.deucher@....com>
Subject: Re: [Nouveau] [PATCH 09/17] drm/radeon: use common fence
 implementation for fences

On Wed, Jul 23, 2014 at 9:37 AM, Christian König
<christian.koenig@....com> wrote:
> Am 23.07.2014 09:31, schrieb Daniel Vetter:
>> On Wed, Jul 23, 2014 at 9:26 AM, Christian König
>> <deathsimple@...afone.de> wrote:
>>>
>>> It's not a locking problem I'm talking about here. Radeons lockup
>>> handling
>>> kicks in when anything calls into the driver from the outside, if you
>>> have a
>>> fence wait function that's called from the outside but doesn't handle
>>> lockups you essentially rely on somebody else calling another radeon
>>> function for the lockup to be resolved.
>>
>> So you don't have a timer in radeon that periodically checks whether
>> progress is still being made? That's the approach we're using in i915,
>> together with some tricks to kick any stuck waiters so that we can
>> reliably step in and grab locks for the reset.
>
>
> We tried this approach, but it didn't worked at all.
>
> I already considered trying it again because of the upcoming fence
> implementation, but reconsidering that when a driver is forced to change
> it's handling because of the fence implementation that's just another hint
> that there is something wrong here.

Out of curiosity: What's the blocker for using a timer/scheduled work
to reset radeon? Getting this right on i915 has been fairly tricky and
we now have an elaborate multi-stage state machine to get the driver
through a reset. So always interested in different solutions.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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