Re: [PATCH RFC 10/18] drm/scheduler: Add can_run_job callback

Daniel Vetter
2023-04-05T14:22:36Z

On Wed, Apr 05, 2023 at 04:14:11PM +0200, Christian König wrote:
> Am 05.04.23 um 15:40 schrieb Daniel Vetter:
> > On Tue, Mar 07, 2023 at 11:25:35PM +0900, Asahi Lina wrote:
> > > Some hardware may require more complex resource utilization accounting
> > > than the simple job count supported by drm_sched internally. Add a
> > > can_run_job callback to allow drivers to implement more logic before
> > > deciding whether to run a GPU job.
> > >
> > > Signed-off-by: Asahi Lina <lina@asahilina.net>
> > Ok scheduler rules, or trying to summarize the entire discussion:
> >
> > dma_fence rules are very tricky. The two main chapters in the docs are
> >
> > https://dri.freedesktop.org/docs/drm/driver-api/dma-buf.html?highlight=dma_buf#dma-fence-cross-driver-contract
> > https://dri.freedesktop.org/docs/drm/driver-api/dma-buf.html?highlight=dma_buf#indefinite-dma-fences
> >
> > Unforutunately I don't think it's possible to check this at compile time,
> > thus far all we can do is validate at runtime. I've posted two patches for
> > this:
> >
> > https://lore.kernel.org/dri-devel/20201023122216.2373294-17-daniel.vetter@ffwll.ch/
> > https://lore.kernel.org/dri-devel/20201023122216.2373294-20-daniel.vetter@ffwll.ch/
> >
> > Unfortunately most drivers are buggy and get this completely wrong, so
> > realistically we'd need to make this a per-driver opt-out and annotate all
> > current drivers. Well except amdgpu is correct by now I think (they'd
> > still need to test that).
>
> There is still one potential memory allocation in the run_job callback in
> amdgpu which I wasn't able to fix yet.
>
> But that one is purely academic and could potentially be trivially replaced
> with using GFP_ATOMIC if we ever have to.

I think the modeset in the tdr code was more scary, and I'm not sure you
really managed to get rid of absolutely everything in there yet.
-Daniel

>
> Christian.
>
> > And Rob Clark is working on patches to fix up
> > msm.
> >
> > I think best here is if you work together with Rob to make sure these
> > annotations are mandatory for any rust drivers (I don't want new buggy
> > drivers at least). Would also be great to improve the kerneldoc for all
> > the driver hooks to explain these restrictions and link to the relevant
> > kerneldocs (there's also one for the dma_fence signalling annotations
> > which might be worth linking too).
> >
> > I don't see any way to make this explicit in rust types, it's really only
> > something runtime tests (using lockdep) can catch. Somewhat disappointing.
> >
> > For the other things discussed here:
> >
> > - Option<Dma_Fence> as the return value for ->prepare_job makes sense to
> > me.
> >
> > - I don't see any way a driver can use ->can_run_job without breaking the
> > above rules, that really doesn't sound like a good idea to me.
> >
> > Cheers, Daniel
> >
> > > ---
> > > drivers/gpu/drm/scheduler/sched_main.c | 10 ++++++++++
> > > include/drm/gpu_scheduler.h | 8 ++++++++
> > > 2 files changed, 18 insertions(+)
> > >
> > > diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c
> > > index 4e6ad6e122bc..5c0add2c7546 100644
> > > --- a/drivers/gpu/drm/scheduler/sched_main.c
> > > +++ b/drivers/gpu/drm/scheduler/sched_main.c
> > > @@ -1001,6 +1001,16 @@ static int drm_sched_main(void *param)
> > > if (!entity)
> > > continue;
> > > + if (sched->ops->can_run_job) {
> > > + sched_job = to_drm_sched_job(spsc_queue_peek(&entity->job_queue));
> > > + if (!sched_job) {
> > > + complete_all(&entity->entity_idle);
> > > + continue;
> > > + }
> > > + if (!sched->ops->can_run_job(sched_job))
> > > + continue;
> > > + }
> > > +
> > > sched_job = drm_sched_entity_pop_job(entity);
> > > if (!sched_job) {
> > > diff --git a/include/drm/gpu_scheduler.h b/include/drm/gpu_scheduler.h
> > > index 9db9e5e504ee..bd89ea9507b9 100644
> > > --- a/include/drm/gpu_scheduler.h
> > > +++ b/include/drm/gpu_scheduler.h
> > > @@ -396,6 +396,14 @@ struct drm_sched_backend_ops {
> > > struct dma_fence *(*prepare_job)(struct drm_sched_job *sched_job,
> > > struct drm_sched_entity *s_entity);
> > > + /**
> > > + * @can_run_job: Called before job execution to check whether the
> > > + * hardware is free enough to run the job. This can be used to
> > > + * implement more complex hardware resource policies than the
> > > + * hw_submission limit.
> > > + */
> > > + bool (*can_run_job)(struct drm_sched_job *sched_job);
> > > +
> > > /**
> > > * @run_job: Called to execute the job once all of the dependencies
> > > * have been resolved. This may be called multiple times, if
> > >
> > > --
> > > 2.35.1
> > >
>

--
Daniel Vetter
Software Engineer, Intel Corporation