Re: [PATCH] drm/nouveau: wait for the exclusive fence after the shared ones v2

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Am 11.12.21 um 10:59 schrieb Stefan Fritsch:
On 09.12.21 11:23, Christian König wrote:
Always waiting for the exclusive fence resulted on some performance
regressions. So try to wait for the shared fences first, then the
exclusive fence should always be signaled already.

v2: fix incorrectly placed "(", add some comment why we do this.

Signed-off-by: Christian König <christian.koenig@xxxxxxx>

Tested-by: Stefan Fritsch <sf@xxxxxxxxxxx>

Thanks.


Please also add a cc for linux-stable, so that this is fixed in 5.15.x

Sure, but I still need some acked-by or rb from one of the Nouveau guys. So gentle ping on that.

Regards,
Christian.


Cheers,
Stefan

---
  drivers/gpu/drm/nouveau/nouveau_fence.c | 28 +++++++++++++------------
  1 file changed, 15 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_fence.c b/drivers/gpu/drm/nouveau/nouveau_fence.c
index 05d0b3eb3690..0ae416aa76dc 100644
--- a/drivers/gpu/drm/nouveau/nouveau_fence.c
+++ b/drivers/gpu/drm/nouveau/nouveau_fence.c
@@ -353,15 +353,22 @@ nouveau_fence_sync(struct nouveau_bo *nvbo, struct nouveau_channel *chan, bool e
            if (ret)
              return ret;
-    }
  -    fobj = dma_resv_shared_list(resv);
-    fence = dma_resv_excl_fence(resv);
+        fobj = NULL;
+    } else {
+        fobj = dma_resv_shared_list(resv);
+    }
  -    if (fence) {
+    /* Waiting for the exclusive fence first causes performance regressions +     * under some circumstances. So manually wait for the shared ones first.
+     */
+    for (i = 0; i < (fobj ? fobj->shared_count : 0) && !ret; ++i) {
          struct nouveau_channel *prev = NULL;
          bool must_wait = true;
  +        fence = rcu_dereference_protected(fobj->shared[i],
+                        dma_resv_held(resv));
+
          f = nouveau_local_fence(fence, chan->drm);
          if (f) {
              rcu_read_lock();
@@ -373,20 +380,13 @@ nouveau_fence_sync(struct nouveau_bo *nvbo, struct nouveau_channel *chan, bool e
            if (must_wait)
              ret = dma_fence_wait(fence, intr);
-
-        return ret;
      }
  -    if (!exclusive || !fobj)
-        return ret;
-
-    for (i = 0; i < fobj->shared_count && !ret; ++i) {
+    fence = dma_resv_excl_fence(resv);
+    if (fence) {
          struct nouveau_channel *prev = NULL;
          bool must_wait = true;
  -        fence = rcu_dereference_protected(fobj->shared[i],
-                        dma_resv_held(resv));
-
          f = nouveau_local_fence(fence, chan->drm);
          if (f) {
              rcu_read_lock();
@@ -398,6 +398,8 @@ nouveau_fence_sync(struct nouveau_bo *nvbo, struct nouveau_channel *chan, bool e
            if (must_wait)
              ret = dma_fence_wait(fence, intr);
+
+        return ret;
      }
        return ret;




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