Commit 7538be3315b8683b05e8f6b22023baadcc0bc4da together
with DRI2/OpenGL triple-buffering support added an
optimization which breaks kms pageflip swap scheduling for most
meaningful use cases and thereby violates the OML_sync_control,
GLX_SGI_swap_control, GLX_swap_control and MESA_swap_control
specs, except for the trivial case of a glXSwapBuffers call
with swap_interval == 1.
This small modification allows to keep the optimization in
the intended way, while removing the hilarious side effects
for timing sensitive applications.
Signed-off-by: Mario Kleiner <mario.kleiner at tuebingen.mpg.de>
---
src/intel_dri.c | 22 +++++++++++++++++++---
1 file changed, 19 insertions(+), 3 deletions(-)
diff --git a/src/intel_dri.c b/src/intel_dri.c
index 126acb2..8786bf4 100644
--- a/src/intel_dri.c
+++ b/src/intel_dri.c
@@ -1275,9 +1275,6 @@ I830DRI2ScheduleSwap(ClientPtr client, DrawablePtr draw, DRI2BufferPtr front,
* the swap.
*/
if (divisor == 0 || current_msc < *target_msc) {
- if (flip && I830DRI2ScheduleFlip(intel, draw, swap_info))
- return TRUE;
-
vbl.request.type =
DRM_VBLANK_ABSOLUTE | DRM_VBLANK_EVENT | pipe_select(pipe);
@@ -1295,6 +1292,25 @@ I830DRI2ScheduleSwap(ClientPtr client, DrawablePtr draw, DRI2BufferPtr front,
if (current_msc >= *target_msc)
*target_msc = current_msc;
+ /* If pageflip is requested for the next possible vblank,
+ * then avoid the roundtrip to the kernels vblank event
+ * delivery and schedule the pageflip for next vblank
+ * directly. This can't be done for any other case, as
+ * it would violate the OML_sync_control spec and
+ * SGI/MESA/GLX_swap_control spec!
+ */
+ if (flip && (current_msc == *target_msc) &&
+ I830DRI2ScheduleFlip(intel, draw, swap_info)) {
+ /* Create approximate target vblank of flip-completion,
+ * so basic consistency checks and swap_interval still
+ * work correctly.
+ */
+ *target_msc += flip;
+ swap_info->frame = *target_msc;
+
+ return TRUE;
+ }
+
vbl.request.sequence = *target_msc;
vbl.request.signal = (unsigned long)swap_info;
ret = drmWaitVBlank(intel->drmSubFD, &vbl);
--
1.7.10.4
