drm/i915/guc: don't spinwait if the GuC's workqueue is full

Rather than wait to see whether more space becomes available in the GuC
submission workqueue, we can just return -EAGAIN and let the caller try
again in a little while. This gets rid of an uninterruptable sleep in
the polling code :)

We'll also add a counter to the GuC client statistics, to see how often
we find the WQ full.

v2:
    Flag the likely() code path (Tvtrko Ursulin).

v4:
    Add/update comments about failure counters (Tvtrko Ursulin).

Signed-off-by: Dave Gordon <david.s.gordon@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

1 files changed, 7 insertions, 11 deletions

diff --git a/drivers/gpu/drm/i915/i915_guc_submission.c b/drivers/gpu/drm/i915/i915_guc_submission.c
index 87cb7396ff93..85b2b89eeb3a 100644
--- a/drivers/gpu/drm/i915/i915_guc_submission.c
+++ b/drivers/gpu/drm/i915/i915_guc_submission.c
@@ -468,26 +468,22 @@ static void guc_fini_ctx_desc(struct intel_guc *guc,
  */
 int i915_guc_wq_check_space(struct drm_i915_gem_request *request)
 {
-	const size_t size = sizeof(struct guc_wq_item);
+	const size_t wqi_size = sizeof(struct guc_wq_item);
 	struct i915_guc_client *gc = request->i915->guc.execbuf_client;
 	struct guc_process_desc *desc;
-	int ret = -ETIMEDOUT, timeout_counter = 200;
+	u32 freespace;
 
 	GEM_BUG_ON(gc == NULL);
 
 	desc = gc->client_base + gc->proc_desc_offset;
 
-	while (timeout_counter-- > 0) {
-		if (CIRC_SPACE(gc->wq_tail, desc->head, gc->wq_size) >= size) {
-			ret = 0;
-			break;
-		}
+	freespace = CIRC_SPACE(gc->wq_tail, desc->head, gc->wq_size);
+	if (likely(freespace >= wqi_size))
+		return 0;
 
-		if (timeout_counter)
-			usleep_range(1000, 2000);
-	};
+	gc->no_wq_space += 1;
 
-	return ret;
+	return -EAGAIN;
 }
 
 static int guc_add_workqueue_item(struct i915_guc_client *gc,