Mesa (master): nouveau: avoid emitting new fences unnecessarily

[Ilia Mirkin]

Module: Mesa
Branch: master
Commit: 8053c9208f30964d89dc4e262fdf2148f0664696
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=8053c9208f30964d89dc4e262fdf2148f0664696

Author: Ilia Mirkin <imirkin at alum.mit.edu>
Date:   Sat Oct 10 01:56:09 2015 -0400

nouveau: avoid emitting new fences unnecessarily

Right now we emit on every kick, but this is only necessary if something
will ever be able to observe that the fence completed. If there are no
refs, leave the fence alone and emit it another day.

This also happens to work around an issue for the kick handler -- a kick
can be a result of e.g. nouveau_bo_wait or explicit kick, or it can be
due to lack of space in the pushbuf. We want the emit to happen in the
current batch, so we want there to always be enough space. However an
explicit kick could take the reserved space for the implicitly-triggered
kick's fence emission if it happened right after. With the new mechanism,
hopefully there's no way to cause two fences to be emitted into the same
reserved space.

Signed-off-by: Ilia Mirkin <imirkin at alum.mit.edu>
Reviewed-by: Samuel Pitoiset <samuel.pitoiset at gmail.com>
Fixes: 47d11990b (nouveau: make sure there's always room to emit a fence)
Cc: mesa-stable at lists.freedesktop.org

---

 src/gallium/drivers/nouveau/nouveau_fence.c |   12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/src/gallium/drivers/nouveau/nouveau_fence.c b/src/gallium/drivers/nouveau/nouveau_fence.c
index ee4e08d..18b1592 100644
--- a/src/gallium/drivers/nouveau/nouveau_fence.c
+++ b/src/gallium/drivers/nouveau/nouveau_fence.c
@@ -190,8 +190,10 @@ nouveau_fence_wait(struct nouveau_fence *fence)
    /* wtf, someone is waiting on a fence in flush_notify handler? */
    assert(fence->state != NOUVEAU_FENCE_STATE_EMITTING);
 
-   if (fence->state < NOUVEAU_FENCE_STATE_EMITTED)
+   if (fence->state < NOUVEAU_FENCE_STATE_EMITTED) {
+      PUSH_SPACE(screen->pushbuf, 8);
       nouveau_fence_emit(fence);
+   }
 
    if (fence->state < NOUVEAU_FENCE_STATE_FLUSHED)
       if (nouveau_pushbuf_kick(screen->pushbuf, screen->pushbuf->channel))
@@ -224,8 +226,12 @@ nouveau_fence_wait(struct nouveau_fence *fence)
 void
 nouveau_fence_next(struct nouveau_screen *screen)
 {
-   if (screen->fence.current->state < NOUVEAU_FENCE_STATE_EMITTING)
-      nouveau_fence_emit(screen->fence.current);
+   if (screen->fence.current->state < NOUVEAU_FENCE_STATE_EMITTING) {
+      if (screen->fence.current->ref > 1)
+         nouveau_fence_emit(screen->fence.current);
+      else
+         return;
+   }
 
    nouveau_fence_ref(NULL, &screen->fence.current);