On 25/03/2020 10:13, Chris Wilson wrote:
We set the priority hint on execlists to avoid executing the tasklet for
when we know that there will be no change in execution order. However,
as we set it from the virtual engine for all siblings, but only one
physical engine may respond, we leave the hint set on the others
stopping direct submission that could take place.

If we do not set the hint, we may attempt direct submission even if we
don't expect to submit. If we set the hint, we may not do any submission
until the tasklet is run (and sometimes we may park the engine before
that has had a chance). Ergo there's only a minor ill-effect on mixed
virtual/physical engine workloads where we may try and fail to do direct
submission more often than required. (Pure virtual / engine workloads
will have redundant tasklet execution suppressed as normal.)

Closes: https://gitlab.freedesktop.org/drm/intel/issues/1522
Signed-off-by: Chris Wilson <ch...@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursu...@intel.com>
  drivers/gpu/drm/i915/gt/intel_lrc.c | 4 +---
  1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c 
index 210f60e14ef4..f88d3b95c4e1 100644
--- a/drivers/gpu/drm/i915/gt/intel_lrc.c
+++ b/drivers/gpu/drm/i915/gt/intel_lrc.c
@@ -4985,10 +4985,8 @@ static void virtual_submission_tasklet(unsigned long 
                node->prio = prio;
-               if (first && prio > sibling->execlists.queue_priority_hint) {
-                       sibling->execlists.queue_priority_hint = prio;
+               if (first && prio > sibling->execlists.queue_priority_hint)
-               }

Reviewed-by: Tvrtko Ursulin <tvrtko.ursu...@intel.com>

The queue_priority_hint scheme with virtual engine design is a bit problematic, since we have no way to unwind. And it's spreading it's tentacles all over the place. Oh well. Could we one day consider just peeking at the top of the tree(s)


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