[PATCH v6] drm/sched: Make sure we wait for all dependencies in kill_jobs_cb()

[Luben Tuikov]

On 2023-06-21 10:53, Boris Brezillon wrote:
> On Wed, 21 Jun 2023 10:41:22 -0400
> Luben Tuikov <luben.tuikov at amd.com> wrote:
> 
>> On 2023-06-21 10:18, Boris Brezillon wrote:
>>> Hello Luben,
>>>
>>> On Wed, 21 Jun 2023 09:56:40 -0400
>>> Luben Tuikov <luben.tuikov at amd.com> wrote:
>>>   
>>>> On 2023-06-19 03:19, Boris Brezillon wrote:  
>>>>> drm_sched_entity_kill_jobs_cb() logic is omitting the last fence popped
>>>>> from the dependency array that was waited upon before
>>>>> drm_sched_entity_kill() was called (drm_sched_entity::dependency field),
>>>>> so we're basically waiting for all dependencies except one.
>>>>>
>>>>> In theory, this wait shouldn't be needed because resources should have
>>>>> their users registered to the dma_resv object, thus guaranteeing that
>>>>> future jobs wanting to access these resources wait on all the previous
>>>>> users (depending on the access type, of course). But we want to keep
>>>>> these explicit waits in the kill entity path just in case.
>>>>>
>>>>> Let's make sure we keep all dependencies in the array in
>>>>> drm_sched_job_dependency(), so we can iterate over the array and wait
>>>>> in drm_sched_entity_kill_jobs_cb().
>>>>>
>>>>> We also make sure we wait on drm_sched_fence::finished if we were
>>>>> originally asked to wait on drm_sched_fence::scheduled. In that case,
>>>>> we assume the intent was to delegate the wait to the firmware/GPU or
>>>>> rely on the pipelining done at the entity/scheduler level, but when
>>>>> killing jobs, we really want to wait for completion not just scheduling.
>>>>>
>>>>> v6:
>>>>> - Back to v4 implementation
>>>>> - Add Christian's R-b
>>>>>
>>>>> v5:
>>>>> - Flag deps on which we should only wait for the scheduled event
>>>>>   at insertion time
>>>>>
>>>>> v4:
>>>>> - Fix commit message
>>>>> - Fix a use-after-free bug
>>>>>
>>>>> v3:
>>>>> - Always wait for drm_sched_fence::finished fences in
>>>>>   drm_sched_entity_kill_jobs_cb() when we see a sched_fence
>>>>>
>>>>> v2:
>>>>> - Don't evict deps in drm_sched_job_dependency()    
>>>>
>>>> Hmm, why is this in reverse chronological order?
>>>> It's very confusing.  
>>>
>>> Dunno, that's how I've always ordered things, and quick look at some
>>> dri-devel patches [1][2] makes me think I'm not the only one to start
>>> from the latest submission.
>>>
>>> [1]https://lkml.org/lkml/2023/6/19/941
>>> [2]https://lore.kernel.org/dri-devel/cover.1686729444.git.Sandor.yu@nxp.com/T/#t
>>>   
>>>>  
>>>>>
>>>>> Signed-off-by: Boris Brezillon <boris.brezillon at collabora.com>
>>>>> Suggested-by: "Christian König" <christian.koenig at amd.com>
>>>>> Reviewed-by: "Christian König" <christian.koenig at amd.com>    
>>>>
>>>> These three lines would usually come after the CCs.  
>>>
>>> Again, I think I've always inserted those tags before the Cc, but I can
>>> re-order things if you prefer. Let me know if you want me to send a v7
>>> addressing the Cc+changelog ordering.  
>>
>> No, it's not necessary for this patch, but in the future I'd rather follow
>> chronological ordering for the versions, and in the Cc list. It's similar
>> to how the patch description follows (narrative text) and to how we reply
>> back to emails, and prevalently in the kernel log in drm ("git log" should
>> suffice).
>>
>> Reading in chronological progression builds a narrative, a picture, in one's
>> mind and makes it easy to see justifications for said narrative, or see reasons
>> to change the narrative.
>>
>> That is, one can make a better decision knowing the full history, rather than
>> only the latest change.
>>
>> (And in fact when I read the version revision list, my eyes skip over v[X]
>> and just read down, so I was wondering why and how Christian R-B the patch
>> in v2, and it wasn't until I actually saw that they were ordered in reverse
>> chronological order, which was in fact v6--listed first, which I'd assumed
>> was listed last.)
>>
>> Do you have access or do you know who is pushing this patch to drm-misc-fixes?
> 
> I can push it.
> 

Acked-by: Luben Tuikov <luben.tuikov at amd.com>

Regards,
Luben