In what seems remarkably similar to the w/a required to not reload an idle context with HEAD==TAIL, it appears we must prevent the HW from switching to an idle context in ELSP[1], while simultaneously trying to preempt the HW to run another context and a continuation of the idle context (which is no longer idle).
We can achieve this by preventing the context from completing while we reload a new ELSP (by applying ring_set_paused(1) across the whole of dequeue), except this eventually fails due to a lite-restore into a waiting semaphore does not generate an ACK. Instead, we try to avoid making the GPU do anything too challenging and not submit a new ELSP while the interrupts + CSB events appear to have fallen behind the completed contexts. We expect it to catch up shortly so we queue another tasklet execution and hope for the best. Closes: https://gitlab.freedesktop.org/drm/intel/issues/1501 Signed-off-by: Chris Wilson <[email protected]> Cc: Tvrtko Ursulin <[email protected]> Cc: Mika Kuoppala <[email protected]> --- drivers/gpu/drm/i915/gt/intel_lrc.c | 26 +++++++++++++++++++++++--- 1 file changed, 23 insertions(+), 3 deletions(-) diff --git a/drivers/gpu/drm/i915/gt/intel_lrc.c b/drivers/gpu/drm/i915/gt/intel_lrc.c index b12355048501..5f17ece07858 100644 --- a/drivers/gpu/drm/i915/gt/intel_lrc.c +++ b/drivers/gpu/drm/i915/gt/intel_lrc.c @@ -1915,11 +1915,26 @@ static void execlists_dequeue(struct intel_engine_cs *engine) * of trouble. */ active = READ_ONCE(execlists->active); - while ((last = *active) && i915_request_completed(last)) - active++; - if (last) { + /* + * In theory we can skip over completed contexts that have not + * yet been processed by events (as those events are in flight): + * + * while ((last = *active) && i915_request_completed(last)) + * active++; + * + * However, the GPU is cannot handle this as it will ultimately + * find itself trying to jump back into a context it has just + * completed and barf. + */ + + if ((last = *active)) { if (need_preempt(engine, last, rb)) { + if (i915_request_completed(last)) { + tasklet_hi_schedule(&execlists->tasklet); + return; + } + ENGINE_TRACE(engine, "preempting last=%llx:%lld, prio=%d, hint=%d\n", last->fence.context, @@ -1947,6 +1962,11 @@ static void execlists_dequeue(struct intel_engine_cs *engine) last = NULL; } else if (need_timeslice(engine, last) && timer_expired(&engine->execlists.timer)) { + if (i915_request_completed(last)) { + tasklet_hi_schedule(&execlists->tasklet); + return; + } + ENGINE_TRACE(engine, "expired last=%llx:%lld, prio=%d, hint=%d\n", last->fence.context, -- 2.20.1 _______________________________________________ Intel-gfx mailing list [email protected] https://lists.freedesktop.org/mailman/listinfo/intel-gfx
