Comment 179 for bug 1098489

Worth trying just:

diff --git a/src/sna/gen4_render.c b/src/sna/gen4_render.c
index 637137e..dc80de3 100644
--- a/src/sna/gen4_render.c
+++ b/src/sna/gen4_render.c
@@ -660,9 +660,11 @@ inline static int gen4_get_rectangles(struct sna *sna,
                if (rem <= 0) {
                        if (sna->render.vertex_offset) {
                                gen4_vertex_flush(sna);
- if (gen4_magic_ca_pass(sna, op))
+ if (gen4_magic_ca_pass(sna, op)) {
+ OUT_BATCH(MI_FLUSH | MI_INHIBIT_RENDER_CACHE_FLUSH);
                                        gen4_emit_pipelined_pointers(sna, op, op->op,
                                                                     op->u.gen4.wm_kernel);
+ }
                        }
                        OUT_BATCH(MI_FLUSH | MI_INHIBIT_RENDER_CACHE_FLUSH);
                        rem = MAX_FLUSH_VERTICES;

if you are happy that it reproduces reliably.