When we retire the last request on the ring, before we ever access that ring again we know it will be completely idle and so we can advance the ring->head fully to the end (i.e. ring->tail) and not just to the start of the breadcrumb. This allows us to skip re-emitting the breadcrumb after resetting the GPU if the ring was entirely idle. This prevents us from overwriting a seqno wraparound by re-executing a stale breadcrumb, i.e. submit_request(1) intel_engine_init_global_seqno(0) i915_reset() would then leave 1 in the HWS, but the next request to execute would also be with seqno 1. The sanity checks upon submission detect this as a timewarp and explode. By setting the ring as empty, upon reset the HWS is left as 0, leaving it consistent with the timeline. v2: Fix check for deleting last element of list. We know that this request is always the first element of the ring, so only if next points back to the start will this be the only request in flight. v3: Remove opencoding of list_is_last() v4: Move the block to its own function for some clarity. Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=100144 Testcase: igt/gem_exec_whisper/hang-* Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> Cc: Mika Kuoppala <mika.kuoppala@xxxxxxxxx> --- drivers/gpu/drm/i915/i915_gem_request.c | 32 ++++++++++++++++++++++---------- 1 file changed, 22 insertions(+), 10 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c index 2f8c5132b54e..313cdff7c6dd 100644 --- a/drivers/gpu/drm/i915/i915_gem_request.c +++ b/drivers/gpu/drm/i915/i915_gem_request.c @@ -271,6 +271,27 @@ void i915_gem_retire_noop(struct i915_gem_active *active, /* Space left intentionally blank */ } +static void advance_ring(struct drm_i915_gem_request *request) +{ + unsigned int tail; + + /* We know the GPU must have read the request to have + * sent us the seqno + interrupt, so use the position + * of tail of the request to update the last known position + * of the GPU head. + * + * Note this requires that we are always called in request + * completion order. + */ + if (list_is_last(&request->ring_link, &request->ring->request_list)) + tail = request->ring->tail; + else + tail = request->postfix; + list_del(&request->ring_link); + + request->ring->head = tail; +} + static void i915_gem_request_retire(struct drm_i915_gem_request *request) { struct intel_engine_cs *engine = request->engine; @@ -287,16 +308,6 @@ static void i915_gem_request_retire(struct drm_i915_gem_request *request) list_del_init(&request->link); spin_unlock_irq(&engine->timeline->lock); - /* We know the GPU must have read the request to have - * sent us the seqno + interrupt, so use the position - * of tail of the request to update the last known position - * of the GPU head. - * - * Note this requires that we are always called in request - * completion order. - */ - list_del(&request->ring_link); - request->ring->head = request->postfix; if (!--request->i915->gt.active_requests) { GEM_BUG_ON(!request->i915->gt.awake); mod_delayed_work(request->i915->wq, @@ -304,6 +315,7 @@ static void i915_gem_request_retire(struct drm_i915_gem_request *request) msecs_to_jiffies(100)); } unreserve_seqno(request->engine); + advance_ring(request); /* Walk through the active list, calling retire on each. This allows * objects to track their GPU activity and mark themselves as idle -- 2.11.0 _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
