Swap watermarks from high (4096) to low (128) when we get full buffers

into the read callback several times in succession; swap back when we
see empty buffers several times. This hopefully limits how much programs
that print a lot for a long period can monopolize tmux (like large, fast
compiling), without penalizing programs that print a lot briefly (like
most curses applications). Helps a lot for me, the actual numbers may
need tweaking later.

tmux.h

@@ -59,8 +59,18 @@ struct tmuxproc;
 /* Automatic name refresh interval, in microseconds. Must be < 1 second. */
 #define NAME_INTERVAL 500000
 
-/* The maximum amount of data to hold from a pty (the event high watermark). */
+/*
-#define READ_SIZE 4096
+ * Event watermarks. We start with FAST then if we hit full size for HITS reads
+ * in succession switch to SLOW, and return when we hit EMPTY the same number
+ * of times.
+ */
+#define READ_FAST_SIZE 4096
+#define READ_SLOW_SIZE 128
+
+#define READ_FULL_SIZE (4096 - 16)
+#define READ_EMPTY_SIZE 16
+
+#define READ_CHANGE_HITS 3
 
 /* Attribute to make gcc check printf-like arguments. */
 #define printflike(a, b) __attribute__ ((format (printf, a, b)))
@@ -884,6 +894,9 @@ struct window_pane {
 	int		 fd;
 	struct bufferevent *event;
 
+	u_int		 wmark_size;
+	u_int		 wmark_hits;
+
 	struct input_ctx *ictx;
 
 	struct grid_cell colgc;

window.c

@@ -56,15 +56,17 @@ struct windows windows;
 
 /* Global panes tree. */
 struct window_pane_tree all_window_panes;
-u_int	next_window_pane_id;
+static u_int	next_window_pane_id;
-u_int	next_window_id;
+static u_int	next_window_id;
-u_int	next_active_point;
+static u_int	next_active_point;
 
-void	window_pane_timer_callback(int, short, void *);
+static void	window_pane_set_watermark(struct window_pane *, size_t);
-void	window_pane_read_callback(struct bufferevent *, void *);
-void	window_pane_error_callback(struct bufferevent *, short, void *);
 
-struct window_pane *window_pane_choose_best(struct window_pane **, u_int);
+static void	window_pane_read_callback(struct bufferevent *, void *);
+static void	window_pane_error_callback(struct bufferevent *, short, void *);
+
+static struct window_pane *window_pane_choose_best(struct window_pane **,
+		    u_int);
 
 RB_GENERATE(windows, window, entry, window_cmp);
 
@@ -809,6 +811,14 @@ window_pane_destroy(struct window_pane *wp)
 	free(wp);
 }
 
+static void
+window_pane_set_watermark(struct window_pane *wp, size_t size)
+{
+	wp->wmark_hits = 0;
+	wp->wmark_size = size;
+	bufferevent_setwatermark(wp->event, EV_READ, 0, size);
+}
+
 int
 window_pane_spawn(struct window_pane *wp, int argc, char **argv,
     const char *path, const char *shell, const char *cwd, struct environ *env,
@@ -915,25 +925,37 @@ window_pane_spawn(struct window_pane *wp, int argc, char **argv,
 	wp->event = bufferevent_new(wp->fd, window_pane_read_callback, NULL,
 	    window_pane_error_callback, wp);
 
-	bufferevent_setwatermark(wp->event, EV_READ, 0, READ_SIZE);
+	window_pane_set_watermark(wp, READ_FAST_SIZE);
 	bufferevent_enable(wp->event, EV_READ|EV_WRITE);
 
 	free(cmd);
 	return (0);
 }
 
-void
+static void
 window_pane_read_callback(__unused struct bufferevent *bufev, void *data)
 {
 	struct window_pane	*wp = data;
 	struct evbuffer		*evb = wp->event->input;
+	size_t			 size = EVBUFFER_LENGTH(evb);
 	char			*new_data;
 	size_t			 new_size;
 
-	log_debug("%%%u has %zu bytes (of %zu)", wp->id, EVBUFFER_LENGTH(evb),
+	if (wp->wmark_size == READ_FAST_SIZE) {
-	    (size_t)READ_SIZE);
+		if (size > READ_FULL_SIZE)
+			wp->wmark_hits++;
+		if (wp->wmark_hits == READ_CHANGE_HITS)
+			window_pane_set_watermark(wp, READ_SLOW_SIZE);
+	} else if (wp->wmark_size == READ_SLOW_SIZE) {
+		if (size < READ_EMPTY_SIZE)
+			wp->wmark_hits++;
+		if (wp->wmark_hits == READ_CHANGE_HITS)
+			window_pane_set_watermark(wp, READ_FAST_SIZE);
+	}
+	log_debug("%%%u has %zu bytes (of %u, %u hits)", wp->id, size,
+	    wp->wmark_size, wp->wmark_hits);
 
-	new_size = EVBUFFER_LENGTH(evb) - wp->pipe_off;
+	new_size = size - wp->pipe_off;
 	if (wp->pipe_fd != -1 && new_size > 0) {
 		new_data = EVBUFFER_DATA(evb) + wp->pipe_off;
 		bufferevent_write(wp->pipe_event, new_data, new_size);
@@ -941,10 +963,10 @@ window_pane_read_callback(__unused struct bufferevent *bufev, void *data)
 
 	input_parse(wp);
 
-	wp->pipe_off = EVBUFFER_LENGTH(evb);
+	wp->pipe_off = size;
 }
 
-void
+static void
 window_pane_error_callback(__unused struct bufferevent *bufev,
     __unused short what, void *data)
 {
@@ -1182,7 +1204,7 @@ window_pane_search(struct window_pane *wp, const char *searchstr,
 }
 
 /* Get MRU pane from a list. */
-struct window_pane *
+static struct window_pane *
 window_pane_choose_best(struct window_pane **list, u_int size)
 {
 	struct window_pane	*next, *best;