uxa: Wakeup 3s after the last rendering to reap the bo-cache

libdrm expires its bo 2s after entry into the cache, but we need to free
a buffer to trigger the reaper. So schedule a timer event to trigger 3s
after the last rendering is submitted to free any resident bo during
long periods of idleness.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>

src/intel.h

@@ -279,6 +279,7 @@ typedef struct intel_screen_private {
 	struct list flush_pixmaps;
 	struct list in_flight;
 	drm_intel_bo *wa_scratch_bo;
+	OsTimerPtr cache_expire;
 
 	/* For Xvideo */
 	Bool use_overlay;

src/intel_driver.c

@@ -1200,6 +1200,9 @@ static Bool I830CloseScreen(int scrnIndex, ScreenPtr screen)
 
 	intel_glamor_close_screen(screen);
 
+	TimerFree(intel->cache_expire);
+	intel->cache_expire = NULL;
+
 	if (intel->uxa_driver) {
 		uxa_driver_fini(screen);
 		free(intel->uxa_driver);

src/intel_uxa.c

@@ -965,6 +965,23 @@ static Bool intel_uxa_get_image(PixmapPtr pixmap,
 	return ret;
 }
 
+static CARD32 intel_cache_expire(OsTimerPtr timer, CARD32 now, pointer data)
+{
+	intel_screen_private *intel = data;
+
+	/* We just want to create and destroy a bo as this causes libdrm
+	 * to reap its caches. However, since we can't remove that buffer
+	 * from the cache due to its own activity, we want to use something
+	 * that we know we will reuse later. The most frequently reused buffer
+	 * we have is the batchbuffer, and the best way to trigger its
+	 * reallocation is to submit a flush.
+	 */
+	intel_batch_emit_flush(intel->scrn);
+	intel_batch_submit(intel->scrn);
+
+	return 0;
+}
+
 static void intel_flush_rendering(intel_screen_private *intel)
 {
 	if (intel->needs_flush == 0)
@@ -978,6 +995,9 @@ static void intel_flush_rendering(intel_screen_private *intel)
 		intel_batch_submit(intel->scrn);
 	}
 
+	intel->cache_expire = TimerSet(intel->cache_expire, 0, 3000,
+				       intel_cache_expire, intel);
+
 	intel->needs_flush = 0;
 }