[PATCH] drm/atomic: Convert a warning to dbg atomic printk

[Michel Dänzer]

On 2022-04-06 16:10, Zack Rusin wrote:
> On Wed, 2022-04-06 at 10:30 +0200, Michel Dänzer wrote:
>> On 2022-04-06 00:47, Zack Rusin wrote:
>>> On Tue, 2022-04-05 at 19:09 +0200, Michel Dänzer wrote:
>>>> On 2022-04-04 20:21, Zack Rusin wrote:
>>>>> From: Zack Rusin <zackr at vmware.com>
>>>>>
>>>>> By default each flip times out after 0.1 sec
>>>>
>>>> 10 * HZ is 10 seconds, not 0.1.
>>>
>>> Yea, sorry, this entire commit message is not correct. I've sent
>>> out a
>>> very old diff with a log the best I could remember. I recall our
>>> conversation now and iirc we said that maybe an interface through
>>> drm
>>> atomic code to enable/disable this error is the way to go but after
>>> looking at this again I'm not sure. More below.
>>>
>>>>> and a warning about the time out is added to the kernel log.
>>>>> The
>>>>> warning is
>>>>> harmless because there's another flip coming right after but it
>>>>> can
>>>>> quickly fill up
>>>>> the log, e.g. missing 2 flips every second over a 24 hour span
>>>>> will
>>>>> add about 172 thousand lines to the log.
>>>>
>>>> As we discussed before, while this might be true for the vmwgfx
>>>> driver,
>>>> for other drivers this message indicates that either the GPU
>>>> hung, or
>>>> something else went wrong spectacularly. As such, I think we do
>>>> want to
>>>> see these messages by default for other drivers at least.
>>>
>>> I'm not going to argue for or against that but I am curious what's
>>> the
>>> point of the message. The message is basically saying "something
>>> could
>>> possibly have went very wrong". OK, what's next? Especially if
>>> there's
>>> no visible problems and it's not reproducible. Even if it would be
>>> reproducible there's nothing actionable from the message itself. If
>>> the
>>> system has no output connected and no users are currently logged in
>>> and
>>> we missed a flip, does it matter?
>>
>> I don't think waiting for a 10 second timeout is the appropriate
>> behaviour in that case. While a KMS CRTC is enabled, the driver needs
>> to make it work, in the worst case via a timer which ticks at the
>> CRTC refresh rate.
> 
> What if it isn't a driver bug

Does it make a difference? It's still a bug.

> and it just so happens that vmwgfx is the only one that's running on some specific system
> without a display long enough?

FWIW, other drivers have hit this same error before as well, but not just because no outputs were enabled. If it's really related to that, a vmwgfx bug seems most likely.


>> The error means that either:
>>
>> * A flip actually didn't complete in 10 seconds.
>> * There's some kind of time tracking issue which results in the timer
>> firing after less than 10 seconds (of the system actually running).
>>
>> Either way, it's an issue which should be fixed rather than just
>> swept under the rug.
> 
> Without being able to reproduce or really confirm that it's an actual
> problem in vmwgfx I'm going to leave this to you then.

Nice try. :) This is for vmwgfx developers.


-- 
Earthling Michel Dänzer            |                  https://redhat.com
Libre software enthusiast          |         Mesa and Xwayland developer