[PATCH 01/55] drm/i915: Reduce breadcrumb lock coverage for intel_engine_enable_signaling()

Chris Wilson
2016-07-25T17:32:59Z

Since intel_engine_enable_signaling() is now only called via
fence_enable_sw_signaling(), we can rely on it to provide serialisation
and run-once for us and so make ourselves slightly simpler.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1469432687-22756-2-git-send-email-chris@chris-wilson.co.uk
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
---
drivers/gpu/drm/i915/intel_breadcrumbs.c | 13 ++++---------
1 file changed, 4 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_breadcrumbs.c b/drivers/gpu/drm/i915/intel_breadcrumbs.c
index d893ccdd62ac..90867446f1a5 100644
--- a/drivers/gpu/drm/i915/intel_breadcrumbs.c
+++ b/drivers/gpu/drm/i915/intel_breadcrumbs.c
@@ -480,19 +480,15 @@ void intel_engine_enable_signaling(struct drm_i915_gem_request *request)
struct rb_node *parent, **p;
bool first, wakeup;

- if (unlikely(READ_ONCE(request->signaling.wait.tsk)))
- return;
-
- spin_lock(&b->lock);
- if (unlikely(request->signaling.wait.tsk)) {
- wakeup = false;
- goto unlock;
- }
+ /* locked by fence_enable_sw_signaling() */
+ assert_spin_locked(&request->lock);

request->signaling.wait.tsk = b->signaler;
request->signaling.wait.seqno = request->fence.seqno;
i915_gem_request_get(request);

+ spin_lock(&b->lock);
+
/* First add ourselves into the list of waiters, but register our
* bottom-half as the signaller thread. As per usual, only the oldest
* waiter (not just signaller) is tasked as the bottom-half waking
@@ -525,7 +521,6 @@ void intel_engine_enable_signaling(struct drm_i915_gem_request *request)
if (first)
smp_store_mb(b->first_signal, request);

-unlock:
spin_unlock(&b->lock);

if (wakeup)
--
2.8.1