Mesa (staging/21.3): iris: implement inter-context busy-tracking

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Module: Mesa
Branch: staging/21.3
Commit: cd51e701177cf01c5590f59071ac1256b396d1b0
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=cd51e701177cf01c5590f59071ac1256b396d1b0

Author: Paulo Zanoni <paulo.r.zanoni at intel.com>
Date:   Mon Jan 10 17:18:05 2022 -0800

iris: implement inter-context busy-tracking

Previously, no buffers were ever marked as EXEC_OBJECT_ASYNC so the
Kernel would ensure dependency tracking for us. After we implemented
explicit busy tracking in commit 89a34cb8450a, only the external
objects kept relying on the Kernel's implicit tracking and Iris did
inter-batch busy tracking, meaning we lost inter-screen and
inter-context synchronization. This seemed fine to me since, as far as
I understood, it is the duty of the application to synchronize itself
against multiple screens and contexts.

The problem here is that applications were actually relying on the old
behavior where the Kernel guarantees synchronization, so 89a34cb8450a
can be seen as a regression. This commit addresses the inter-context
synchronization case.

Cc: mesa-stable
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/5731
Closes: https://gitlab.freedesktop.org/mesa/mesa/-/issues/5812
Fixes: 89a34cb8450a ("iris: switch to explicit busy tracking")
Tested-by: Konstantin Kharlamov <hi-angel at yandex.ru>
Reviewed-by: Kenneth Graunke <kenneth at whitecape.org>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni at intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/14783>

---

 .pick_status.json                     | 2 +-
 src/gallium/drivers/iris/iris_batch.c | 8 ++++++++
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/.pick_status.json b/.pick_status.json
index d325da5ae33..e831bd32b72 100644
--- a/.pick_status.json
+++ b/.pick_status.json
@@ -742,7 +742,7 @@
         "description": "iris: implement inter-context busy-tracking",
         "nominated": true,
         "nomination_type": 1,
-        "resolution": 0,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": "89a34cb8450a6fdaceb0e537613871fa86d93132"
     },
diff --git a/src/gallium/drivers/iris/iris_batch.c b/src/gallium/drivers/iris/iris_batch.c
index ef0fa147d38..90103449bf1 100644
--- a/src/gallium/drivers/iris/iris_batch.c
+++ b/src/gallium/drivers/iris/iris_batch.c
@@ -717,6 +717,12 @@ update_bo_syncobjs(struct iris_batch *batch, struct iris_bo *bo, bool write)
       move_syncobj_to_batch(batch, &deps->write_syncobjs[other_batch_idx],
                             I915_EXEC_FENCE_WAIT);
 
+   /* If it's being written by our screen, wait on it too. This is relevant
+    * when there are multiple contexts on the same screen. */
+   if (deps->write_syncobjs[batch_idx])
+      move_syncobj_to_batch(batch, &deps->write_syncobjs[batch_idx],
+                            I915_EXEC_FENCE_WAIT);
+
    struct iris_syncobj *batch_syncobj = iris_batch_get_signal_syncobj(batch);
 
    if (write) {
@@ -729,6 +735,8 @@ update_bo_syncobjs(struct iris_batch *batch, struct iris_bo *bo, bool write)
 
       move_syncobj_to_batch(batch, &deps->read_syncobjs[other_batch_idx],
                            I915_EXEC_FENCE_WAIT);
+      move_syncobj_to_batch(batch, &deps->read_syncobjs[batch_idx],
+                           I915_EXEC_FENCE_WAIT);
 
    } else {
       /* If we're reading, replace the other read from our batch index. */