Fix unnecessary threaded rendering frame drops

When DMA requests force a background queue flush, the update lace
handler can no longer know there was a pending frame. If this happens
often enough, it can delay the next frame indefinitely.

Whenever the background queue is emptied, the next update_lace needs
to force a render.

diff --git a/plugins/gpulib/gpulib_thread_if.c b/plugins/gpulib/gpulib_thread_if.c
index c95f529..1583783 100644 (file)
--- a/plugins/gpulib/gpulib_thread_if.c
+++ b/plugins/gpulib/gpulib_thread_if.c
@@ -60,6 +60,7 @@ static video_thread_queue queues[2];
 static int thread_rendering;
 static BOOL hold_cmds;
 static BOOL needs_display;
+static BOOL flushed;
 
 extern const unsigned char cmd_lengths[];
 
@@ -132,7 +133,6 @@ static void cmd_queue_swap() {
                tmp = thread.queue;
                thread.queue = thread.bg_queue;
                thread.bg_queue = tmp;
-               needs_display = TRUE;
                pthread_cond_signal(&thread.cond_msg_avail);
        }
        pthread_mutex_unlock(&thread.queue_lock);
@@ -168,6 +168,13 @@ void renderer_sync(void) {
                return;
        }
 
+       if (thread.bg_queue->used) {
+               /* When we flush the background queue, the vblank handler can't
+                * know that we had a frame pending, and we delay rendering too
+                * long. Force it. */
+               flushed = TRUE;
+       }
+
        /* Flush both queues. This is necessary because gpulib could be
         * trying to process a DMA write that a command in the queue should
         * run beforehand. For example, Xenogears sprites write a black
@@ -433,7 +440,7 @@ void renderer_notify_update_lace(int updated) {
        }
 
        pthread_mutex_lock(&thread.queue_lock);
-       if (thread.bg_queue->used) {
+       if (thread.bg_queue->used || flushed) {
                /* We have commands for a future frame to run. Force a wait until
                 * the current frame is finished, and start processing the next
                 * frame after it's drawn (see the `updated` clause above). */
@@ -444,6 +451,7 @@ void renderer_notify_update_lace(int updated) {
                /* We are no longer holding commands back, so the next frame may
                 * get mixed into the following frame. This is usually fine, but can
                 * result in frameskip-like effects for 60fps games. */
+               flushed = FALSE;
                hold_cmds = FALSE;
                needs_display = TRUE;
                gpu.state.fb_dirty = TRUE;