From 67f74302f45d5d862f22ced3297624e50ac352f0 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Christian=20K=C3=B6nig?= <christian.koenig@amd.com>
Date: Tue, 7 Dec 2021 10:10:15 +0100
Subject: drm/nouveau: wait for the exclusive fence after the shared ones v2
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Git-commit: 67f74302f45d5d862f22ced3297624e50ac352f0
Patch-mainline: v5.16-rc8
References: bsc#1152472

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@amd.com>
Tested-by: Stefan Fritsch <sf@sfritsch.de>
Tested-by: Dan Moulding <dmoulding@me.com>
Acked-by: Ben Skeggs <bskeggs@redhat.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Cc: <stable@vger.kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20211209102335.18321-1-christian.koenig@amd.com
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
---
 drivers/gpu/drm/nouveau/nouveau_fence.c |   27 ++++++++++++++-------------
 1 file changed, 14 insertions(+), 13 deletions(-)

--- a/drivers/gpu/drm/nouveau/nouveau_fence.c
+++ b/drivers/gpu/drm/nouveau/nouveau_fence.c
@@ -353,15 +353,21 @@ nouveau_fence_sync(struct nouveau_bo *nv
 
 		if (ret)
 			return ret;
+		fobj = NULL;
+	} else {
+		fobj = dma_resv_shared_list(resv);
 	}
 
-	fobj = dma_resv_shared_list(resv);
-	fence = dma_resv_excl_fence(resv);
-
-	if (fence && (!exclusive || !fobj || !fobj->shared_count)) {
+	/* 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 +379,13 @@ nouveau_fence_sync(struct nouveau_bo *nv
 
 		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 +397,8 @@ nouveau_fence_sync(struct nouveau_bo *nv
 
 		if (must_wait)
 			ret = dma_fence_wait(fence, intr);
+
+		return ret;
 	}
 
 	return ret;