Re: [PATCH 1/4] drm/sched: Mark scheduler work queues with WQ_MEM_RECLAIM

[Matthew Brost <matthew.brost@intel.com>]

On Tue, Oct 22, 2024 at 04:19:18PM +0200, Philipp Stanner wrote:
> On Mon, 2024-10-21 at 10:57 -0700, Matthew Brost wrote:
> > DRM scheduler work queues are used to submit jobs, jobs are in the
> > path
> 
> "scheduler work queues" is very generic, how about
> "drm_gpu_scheduler.submit_wq is used to submit jobs, [...]"
> 

Sure.

> > or dma-fences, and dma-fences are in the path of reclaim. Mark
> 
> s/or/of
> 

Yep.

> > scheduler
> > work queues with WQ_MEM_RECLAIM so these work queues can continue to
> > make forward progress during reclaim.
> 
> It is just *one* queue (per scheduler) really, isn't it?
> 

Yes.

> If the change above is applied, could just say: "Create the work queue
> with WQ_MEM_RECLAIM so it can continue [...]"
> 

Now you are confusing me.

> So for my understanding: is this a performance optimization or is it a
> bug? IOW, would forward progress just be delayed or entirely prevented?
> Would be cool to state that a bit more clearly in the commit message.
> 

I can make that a bit more clear.

> Work-queue docu says "MUST":
> 
> ``WQ_MEM_RECLAIM`` All wq which might be used in the memory reclaim
> paths **MUST** have this flag set. The wq is guaranteed to have at
> least one execution context regardless of memory pressure.
> 
> So it seems to me that this fixes a bug? Should it be backported in
> your opinion?
> 

Bug - yea probably a fix tag then for backporting. Will add in next rev.

> 
> > 
> > Cc: Luben Tuikov <ltuikov89@gmail.com>
> 
> btw., how did you send this email? I couldn't find Luben on CC. Added
> him.

git send-email...

I may have forgot to include him on the Cc list.

Matt

> 
> Thx,
> P.
> 
> > Cc: Danilo Krummrich <dakr@kernel.org>
> > Cc: Philipp Stanner <pstanner@redhat.com>
> > Signed-off-by: Matthew Brost <matthew.brost@intel.com>
> > ---
> >  drivers/gpu/drm/scheduler/sched_main.c | 4 ++--
> >  1 file changed, 2 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/gpu/drm/scheduler/sched_main.c
> > b/drivers/gpu/drm/scheduler/sched_main.c
> > index 6e4d004d09ce..567811957c0f 100644
> > --- a/drivers/gpu/drm/scheduler/sched_main.c
> > +++ b/drivers/gpu/drm/scheduler/sched_main.c
> > @@ -1275,10 +1275,10 @@ int drm_sched_init(struct drm_gpu_scheduler
> > *sched,
> >   sched->own_submit_wq = false;
> >   } else {
> >  #ifdef CONFIG_LOCKDEP
> > - sched->submit_wq = alloc_ordered_workqueue_lockdep_map(name, 0,
> > + sched->submit_wq = alloc_ordered_workqueue_lockdep_map(name,
> > WQ_MEM_RECLAIM,
> >          &drm_sched_lockdep_map);
> >  #else
> > - sched->submit_wq = alloc_ordered_workqueue(name, 0);
> > + sched->submit_wq = alloc_ordered_workqueue(name, WQ_MEM_RECLAIM);
> >  #endif
> >   if (!sched->submit_wq)
> >   return -ENOMEM;
>