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. Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=100144 Testcase: igt/gem_exec_whisper/hang-* Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> --- drivers/gpu/drm/i915/i915_gem_request.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/drivers/gpu/drm/i915/i915_gem_request.c b/drivers/gpu/drm/i915/i915_gem_request.c index 2f8c5132b54e..e535036132b0 100644 --- a/drivers/gpu/drm/i915/i915_gem_request.c +++ b/drivers/gpu/drm/i915/i915_gem_request.c @@ -295,8 +295,11 @@ static void i915_gem_request_retire(struct drm_i915_gem_request *request) * Note this requires that we are always called in request * completion order. */ + if (request->ring_link.next == &request->ring->request_list) + request->ring->head = request->ring->tail; + else + request->ring->head = request->postfix; 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, -- 2.11.0 _______________________________________________ Intel-gfx mailing list Intel-gfx@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/intel-gfx
