i965: Order write of query availablity with earlier writes

Currently we signal the availabilty of the query result using an
unordered pipe-control write. As it is unordered, it may be executed
before the write of the query result itself - and so an observer may
read the query result too early. Fix this by requesting that the write
of the availablity flag is ordered after earlier pipe control writes.

Testcase: piglit/arb_query_buffer_object-qbo/*async*
Signed-off-by: Chris Wilson <[email protected]>
Reviewed-by: Alejandro Piñeiro <[email protected]>

1 files changed, 11 insertions, 2 deletions

diff --git a/src/mesa/drivers/dri/i965/gen6_queryobj.c b/src/mesa/drivers/dri/i965/gen6_queryobj.c
index cb4f46c28be..a28f83af1d6 100644
--- a/src/mesa/drivers/dri/i965/gen6_queryobj.c
+++ b/src/mesa/drivers/dri/i965/gen6_queryobj.c
@@ -60,8 +60,17 @@ set_query_availability(struct brw_context *brw, struct brw_query_object *query,
     */
    if (brw->ctx.Extensions.ARB_query_buffer_object &&
        brw_is_query_pipelined(query)) {
-      brw_emit_pipe_control_write(brw,
-                                  PIPE_CONTROL_WRITE_IMMEDIATE,
+      unsigned flags = PIPE_CONTROL_WRITE_IMMEDIATE;
+
+      if (available) {
+         /* Order available *after* the query results. */
+         flags |= PIPE_CONTROL_FLUSH_ENABLE;
+      } else {
+         /* Make it unavailable *before* any pipelined reads. */
+         flags |= PIPE_CONTROL_CS_STALL;
+      }
+
+      brw_emit_pipe_control_write(brw, flags,
                                   query->bo, 2 * sizeof(uint64_t),
                                   available, 0);
    }