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

[Boris Brezillon <boris.brezillon@collabora.com>]

On Wed, 21 Jun 2023 10:41:22 -0400
Luben Tuikov <luben.tuikov@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@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@collabora.com>
> >>> Suggested-by: "Christian König" <christian.koenig@amd.com>
> >>> Reviewed-by: "Christian König" <christian.koenig@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.