server 1.7 EXA and R600 UploadToScreen infinite loop

[Michel Dänzer]

On Wed, 2009-09-30 at 13:08 +1000, Dave Airlie wrote: 
> 
> So I've been getting a recusive problem with 1.7's EXA (not with master)
> 0369eeeb6bf8a808fa2df503fc8b8df81e6e07b8 works around the issue.
> 
> What seems to be happening is the r600 UTS has an "optimisation" (Alex did
> you write it?)
> 
>     /* If we know the BO won't be busy, don't bother */
>     if (driver_priv->bo->cref == 1 &&
>     	!radeon_bo_is_busy(driver_priv->bo, &dst_domain))
>     	return FALSE;
> 
> Now we get into a cycle, as shown below, the EXA core tries to migrate
> to the FB, UTS fails it fallbacks to doing prepare/memcpy/finish, finish
> notices dirty status, and tries to upload to screen again, which fallsback
> to doing prepare/memcpy/finish, etc.
> 
> The patch in master works around this of course, however I've no idea whether
> a) that is in fact the correct solution

I'm not sure it can prevent the problem in all cases.

Does the patch below help? The idea is to move the FinishAccess call
after the valid region updates in exaCopyDirty(), so the second call of
that should be a no-op. It would be better to stop the recursion
earlier, but I don't have any good ideas offhand.


diff --git a/exa/exa_migration_classic.c b/exa/exa_migration_classic.c
index 4819af8..6d7b9f5 100644
--- a/exa/exa_migration_classic.c
+++ b/exa/exa_migration_classic.c
@@ -242,11 +242,6 @@ exaCopyDirty(ExaMigrationPtr migrate, RegionPtr pValidDst, RegionPtr pValidSrc,
 	pBox++;
     }
 
-    if (access_prepared)
-	exaFinishAccess(&pPixmap->drawable, fallback_index);
-    else if (need_sync && sync)
-	sync (pPixmap->drawable.pScreen);
-
     pExaPixmap->offscreen = save_offscreen;
     pPixmap->devKind = save_pitch;
 
@@ -261,6 +256,11 @@ exaCopyDirty(ExaMigrationPtr migrate, RegionPtr pValidDst, RegionPtr pValidSrc,
     REGION_UNION(pScreen, pValidDst, pValidDst, &CopyReg);
 
     REGION_UNINIT(pScreen, &CopyReg);
+
+    if (access_prepared)
+	exaFinishAccess(&pPixmap->drawable, fallback_index);
+    else if (need_sync && sync)
+	sync (pPixmap->drawable.pScreen);
 }
 
 /**


-- 
Earthling Michel Dänzer           |                http://www.vmware.com
Libre software enthusiast         |          Debian, X and DRI developer