Bug 20797

With -intel 2.6.3 performance was very bad when using a non gem enabled kernel (2.6.27) and EXA. For example sauerbraten ran with 4 fps and screensaver GLBlur with 1 fps. With -intel 2.6.1 performance was good using the same kernel.

Git bisecting led me to commit f1ed73c1ef3e3daa9f695194dcc813167cbcb53d (in 2.6 branch) "Make i830_allocate_memory take tiling parameters" as first bad commit.

Using gdb I found tiling was set exactly the same in 2.6.3 as in 2.6.1, so that was good (TILE_XMAJOR for front, back and depth buffers).
Looking further I found the line mem->tiling = TILE_NONE; (line 961 in src/i830_memory.c) at the end of i830_allocate_memory suspicious, as mem->tiling now already gets set via i830_allocate_aperture and some buffers do have tiling. Removing that line indeed fixed the performance issue. Now sauerbraten runs with 30+ fps and GLBlur runs smoothly.


diff against git master:

diff --git a/src/i830_memory.c b/src/i830_memory.c
index 052d906..e3314c5 100644
--- a/src/i830_memory.c
+++ b/src/i830_memory.c
@@ -958,8 +958,6 @@ i830_allocate_memory(ScrnInfoPtr pScrn, const char *name,
        }
     }

-    mem->tiling = TILE_NONE;
-
     return mem;
 }