[RFC 00/10] Virtual queue/engine uAPI prototype

Tvrtko Ursulin
2018-01-25T13:33:44Z

The latest idea on how to load-balance VCS submissions in i915.

This time round we have a concept of submission queues implemented as contexts
which share PPGTT.

Userspace is supposed to create a queue with the virtual flag set to one.
Subsequent submissions to this queue will be load-balanced between available VCS
engines by the driver.

Only new class/instance based execbuf uAPI is supported. Explicit VCS engine
selection will be rejected meaning engine instance must be set to zero.

Engine capabilities must be used if a submission depends on an non-uniform
engine feature like HEVC which is only available on VCS0.

This series is just a prototype which illustrates the uAPI proposal. It does not
claim to balance well. In fact, it is known to balance poorly - in some cases
significantly worse than the same approach implemented in userspace. This
potentially stems from the fact it creates a forced dependency when moving
between engines (even when there are no data dependencies between batches) in
order to simulate a single stream of execution per virtual engine.

Series also doesn't implement the virtual engine fully in a way that context
state does not move around with the submissions, ie. it is not preserved.

I will also post gem_wsim and media-bench.pl IGT patches which allows playing
with this easily.

Chris Wilson (2):
move-timeline-to-ctx
drm/i915: Extend CREATE_CONTEXT to allow inheritance ala clone()

Tvrtko Ursulin (8):
drm/i915: Select engines via class and instance in execbuffer2
drm/i915: Engine capabilities uAPI
drm/i915: Re-arrange execbuf so context is known before engine
drm/i915: Refactor eb_select_engine to take eb
drm/i915: Track latest request per engine class
drm/i915: Allow creating virtual contexts
drm/i915: Trivial virtual engine implementation
drm/i915: Naive engine busyness based load balancing

drivers/gpu/drm/i915/i915_drv.h | 11 +-
drivers/gpu/drm/i915/i915_gem.c | 9 +-
drivers/gpu/drm/i915/i915_gem_context.c | 91 +++++++--
drivers/gpu/drm/i915/i915_gem_context.h | 23 +++
drivers/gpu/drm/i915/i915_gem_execbuffer.c | 223 ++++++++++++++++----
drivers/gpu/drm/i915/i915_gem_gtt.c | 7 +-
drivers/gpu/drm/i915/i915_gem_gtt.h | 2 -
drivers/gpu/drm/i915/i915_gem_request.c | 15 +-
drivers/gpu/drm/i915/i915_gem_request.h | 2 +
drivers/gpu/drm/i915/i915_gem_timeline.c | 66 +++++-
drivers/gpu/drm/i915/i915_gem_timeline.h | 6 +
drivers/gpu/drm/i915/intel_engine_cs.c | 41 +++-
drivers/gpu/drm/i915/intel_lrc.c | 2 +-
drivers/gpu/drm/i915/intel_ringbuffer.c | 9 +-
drivers/gpu/drm/i915/intel_ringbuffer.h | 9 +-
drivers/gpu/drm/i915/selftests/huge_pages.c | 1 -
drivers/gpu/drm/i915/selftests/i915_gem_context.c | 236 +++++++++++++++++-----
drivers/gpu/drm/i915/selftests/i915_gem_gtt.c | 1 -
drivers/gpu/drm/i915/selftests/mock_context.c | 3 +-
drivers/gpu/drm/i915/selftests/mock_engine.c | 3 +-
drivers/gpu/drm/i915/selftests/mock_gem_device.c | 4 +-
drivers/gpu/drm/i915/selftests/mock_gtt.c | 1 -
include/uapi/drm/i915_drm.h | 38 +++-
23 files changed, 660 insertions(+), 143 deletions(-)