Re: [RFC 00/14] Deadline scheduler and other ideas

[Danilo Krummrich <dakr@redhat.com>]

On Mon, Dec 30, 2024 at 04:52:45PM +0000, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>

"Deadline scheduler and other ideas"

There's a few patches that could be sent outside the scope of this series, e.g.
the first one.

I think it would make sense to do so.

> 
> <tldr>
> Replacing FIFO with a flavour of deadline driven scheduling and removing round-
> robin. Connecting the scheduler with dma-fence deadlines. First draft and
> testing by different drivers and feedback would be nice. I was only able to test
> it with amdgpu. Other drivers may not even compile.

What are the results from your tests with amdgpu? Do you have some measurements?

> </tldr>
> 
> If I remember correctly Christian mentioned recently (give or take) that maybe
> round-robin could be removed. That got me thinking how and what could be
> improved and simplified. So I played a bit in the scheduler code and came up
> with something which appears to not crash at least. Whether or not there are
> significant advantages apart from maybe code consolidation and reduction is the
> main thing to be determined.
> 
> One big question is whether round-robin can really be removed. Does anyone use
> it, rely on it, or what are even use cases where it is much better than FIFO.
> 
> See "drm/sched: Add deadline policy" commit message for a short description on
> what flavour of deadline scheduling it is. But in essence it should a more fair
> FIFO where higher priority can not forever starve lower priorities.
> 
> "drm/sched: Connect with dma-fence deadlines" wires up dma-fence deadlines to
> the scheduler because it is easy and makes logical sense with this. And I
> noticed userspace already uses it so why not wire it up fully.
> 
> Otherwise the series is a bit of progression from consolidating RR into FIFO
> code paths and going from there to deadline and then to a change in how
> dependencies are handled. And code simplification to 1:1 run queue to scheduler
> relationship, because deadline does not need per priority run queues.
> 
> There is quite a bit of code to go throught here so I think it could be even
> better if other drivers could give it a spin as is and see if some improvements
> can be detected. Or at least no regressions.

Are there improvements with amdgpu?

> 
> Cc: Christian König <christian.koenig@amd.com>
> Cc: Danilo Krummrich <dakr@redhat.com>
> Cc: Matthew Brost <matthew.brost@intel.com>
> Cc: Philipp Stanner <pstanner@redhat.com>
> 
> Tvrtko Ursulin (14):
>   drm/sched: Delete unused update_job_credits
>   drm/sched: Remove idle entity from tree
>   drm/sched: Implement RR via FIFO
>   drm/sched: Consolidate entity run queue management
>   drm/sched: Move run queue related code into a separate file
>   drm/sched: Ignore own fence earlier
>   drm/sched: Resolve same scheduler dependencies earlier
>   drm/sched: Add deadline policy
>   drm/sched: Remove FIFO and RR and simplify to a single run queue
>   drm/sched: Queue all free credits in one worker invocation
>   drm/sched: Connect with dma-fence deadlines
>   drm/sched: Embed run queue singleton into the scheduler
>   dma-fence: Add helper for custom fence context when merging fences
>   drm/sched: Resolve all job dependencies in one go
> 
>  drivers/dma-buf/dma-fence-unwrap.c          |   8 +-
>  drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c      |   6 +-
>  drivers/gpu/drm/amd/amdgpu/amdgpu_job.c     |  27 +-
>  drivers/gpu/drm/amd/amdgpu/amdgpu_job.h     |   5 +-
>  drivers/gpu/drm/amd/amdgpu/amdgpu_trace.h   |   8 +-
>  drivers/gpu/drm/amd/amdgpu/amdgpu_vm_sdma.c |   8 +-
>  drivers/gpu/drm/amd/amdgpu/amdgpu_xcp.c     |   8 +-
>  drivers/gpu/drm/scheduler/Makefile          |   2 +-
>  drivers/gpu/drm/scheduler/sched_entity.c    | 316 ++++++-----
>  drivers/gpu/drm/scheduler/sched_fence.c     |   5 +-
>  drivers/gpu/drm/scheduler/sched_main.c      | 587 +++++---------------
>  drivers/gpu/drm/scheduler/sched_rq.c        | 199 +++++++
>  include/drm/gpu_scheduler.h                 |  74 ++-
>  include/linux/dma-fence-unwrap.h            |  31 +-
>  14 files changed, 606 insertions(+), 678 deletions(-)
>  create mode 100644 drivers/gpu/drm/scheduler/sched_rq.c
> 
> -- 
> 2.47.1
>