From 0d90ccb70211cbf55140e91bd39db684aa4c16e9 Mon Sep 17 00:00:00 2001 From: Chris Wilson Date: Wed, 1 May 2019 12:45:36 +0100 Subject: [PATCH] drm/i915: Delay semaphore submission until the start of the signaler Currently we submit the semaphore busywait as soon as the signaler is submitted to HW. However, we may submit the signaler as the tail of a batch of requests, and even not as the first context in the HW list, i.e. the busywait may start spinning far in advance of the signaler even starting. If we wait until the request before the signaler is completed before submitting the busywait, we prevent the busywait from starting too early, if the signaler is not first in submission port. To handle the case where the signaler is at the start of the second (or later) submission port, we will need to delay the execution callback until we know the context is promoted to port0. A challenge for later. Fixes: e88619646971 ("drm/i915: Use HW semaphores for inter-engine synchroni sation on gen8+") Signed-off-by: Chris Wilson Cc: Tvrtko Ursulin Reviewed-by: Tvrtko Ursulin Link: https://patchwork.freedesktop.org/patch/msgid/20190501114541.10077-9-chris@chris-wilson.co.uk --- drivers/gpu/drm/i915/i915_request.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/drivers/gpu/drm/i915/i915_request.c b/drivers/gpu/drm/i915/i915_request.c index af8c9fa5e066..d06c45305b03 100644 --- a/drivers/gpu/drm/i915/i915_request.c +++ b/drivers/gpu/drm/i915/i915_request.c @@ -770,6 +770,21 @@ err_unlock: return rq; } +static int +i915_request_await_start(struct i915_request *rq, struct i915_request *signal) +{ + if (list_is_first(&signal->ring_link, &signal->ring->request_list)) + return 0; + + signal = list_prev_entry(signal, ring_link); + if (i915_timeline_sync_is_later(rq->timeline, &signal->fence)) + return 0; + + return i915_sw_fence_await_dma_fence(&rq->submit, + &signal->fence, 0, + I915_FENCE_GFP); +} + static int emit_semaphore_wait(struct i915_request *to, struct i915_request *from, @@ -788,6 +803,10 @@ emit_semaphore_wait(struct i915_request *to, &from->fence, 0, I915_FENCE_GFP); + err = i915_request_await_start(to, from); + if (err < 0) + return err; + err = i915_sw_fence_await_dma_fence(&to->semaphore, &from->fence, 0, I915_FENCE_GFP);