[RFC v2 00/18] Deadline scheduler and other ideas

[Tvrtko Ursulin]

<tldr>
Replacing FIFO with a flavour of deadline driven scheduling and removing round-
robin. Connecting the scheduler with dma-fence deadlines. Second 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.
</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 trivial cleanups to
consolidating RR into FIFO code paths and going from there to deadline and then
some 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.

v2:
 * Fixed many rebase errors.
 * Added some new patches.
 * Dropped single shot dependecy handling.

Cc: Christian König <christian.koenig at amd.com>
Cc: Danilo Krummrich <dakr at redhat.com>
Cc: Matthew Brost <matthew.brost at intel.com>
Cc: Philipp Stanner <pstanner at redhat.com>

Tvrtko Ursulin (18):
  drm/amdgpu: Use DRM scheduler API in amdgpu_xcp_release_sched
  drm/sched: Delete unused update_job_credits
  drm/sched: Remove one local variable
  drm/sched: Remove weak paused submission checks
  drm/sched: Avoid double re-lock on the job free path
  drm/sched: Add helper to check job dependencies
  drm/imagination: Use the drm_sched_job_has_dependency helper
  drm/sched: Clarify locked section in drm_sched_rq_select_entity_fifo
  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: 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
  drm/sched: Scale deadlines depending on queue depth

 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     |  10 +-
 drivers/gpu/drm/imagination/pvr_job.c       |  12 +-
 drivers/gpu/drm/scheduler/Makefile          |   2 +-
 drivers/gpu/drm/scheduler/sched_entity.c    | 147 +++---
 drivers/gpu/drm/scheduler/sched_fence.c     |   2 +-
 drivers/gpu/drm/scheduler/sched_main.c      | 541 ++++----------------
 drivers/gpu/drm/scheduler/sched_rq.c        | 177 +++++++
 include/drm/gpu_scheduler.h                 |  55 +-
 13 files changed, 424 insertions(+), 576 deletions(-)
 create mode 100644 drivers/gpu/drm/scheduler/sched_rq.c

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2.47.1