drm/i915: Skip request serialisation if the timeline is already complete

If the last request on the timeline is already complete, we do not need
to emit the serialisation barriers.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180207084350.3929-2-chris@chris-wilson.co.uk

diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c
index 8efa9e7a9e4672a04857d7c154ef258c2c2687dd..e5f87629e71810bd4a9fe0cc9002ceb162eb0c49 100644 (file)
--- a/drivers/gpu/drm/i915/i915_gem_request.c
+++ b/drivers/gpu/drm/i915/i915_gem_request.c
@@ -993,7 +993,8 @@ void __i915_add_request(struct drm_i915_gem_request *request, bool flush_caches)
        lockdep_assert_held(&request->i915->drm.struct_mutex);
        trace_i915_gem_request_add(request);
 
-       /* Make sure that no request gazumped us - if it was allocated after
+       /*
+        * Make sure that no request gazumped us - if it was allocated after
         * our i915_gem_request_alloc() and called __i915_add_request() before
         * us, the timeline will hold its seqno which is later than ours.
         */
@@ -1020,7 +1021,8 @@ void __i915_add_request(struct drm_i915_gem_request *request, bool flush_caches)
                WARN(err, "engine->emit_flush() failed: %d!\n", err);
        }
 
-       /* Record the position of the start of the breadcrumb so that
+       /*
+        * Record the position of the start of the breadcrumb so that
         * should we detect the updated seqno part-way through the
         * GPU processing the request, we never over-estimate the
         * position of the ring's HEAD.
@@ -1029,7 +1031,8 @@ void __i915_add_request(struct drm_i915_gem_request *request, bool flush_caches)
        GEM_BUG_ON(IS_ERR(cs));
        request->postfix = intel_ring_offset(request, cs);
 
-       /* Seal the request and mark it as pending execution. Note that
+       /*
+        * Seal the request and mark it as pending execution. Note that
         * we may inspect this state, without holding any locks, during
         * hangcheck. Hence we apply the barrier to ensure that we do not
         * see a more recent value in the hws than we are tracking.
@@ -1037,7 +1040,7 @@ void __i915_add_request(struct drm_i915_gem_request *request, bool flush_caches)
 
        prev = i915_gem_active_raw(&timeline->last_request,
                                   &request->i915->drm.struct_mutex);
-       if (prev) {
+       if (prev && !i915_gem_request_completed(prev)) {
                i915_sw_fence_await_sw_fence(&request->submit, &prev->submit,
                                             &request->submitq);
                if (engine->schedule)
@@ -1057,7 +1060,8 @@ void __i915_add_request(struct drm_i915_gem_request *request, bool flush_caches)
        list_add_tail(&request->ring_link, &ring->request_list);
        request->emitted_jiffies = jiffies;
 
-       /* Let the backend know a new request has arrived that may need
+       /*
+        * Let the backend know a new request has arrived that may need
         * to adjust the existing execution schedule due to a high priority
         * request - i.e. we may want to preempt the current request in order
         * to run a high priority dependency chain *before* we can execute this