overlay: short-circuit draw_heirarchy_row() if unchanged

If vmon hasn't seen any heirarchical changes, and we aren't forcing a redraw,
and the process information being shown isn't changed, don't bother
re-rendering the same thing the overlay already contains.

This can be further improved, like if only wchan changed and nothing else, only
redraw the wchan column for the relevant row.  It gets tricky quickly though,
because a new wchan could be wider than the column currently permits for
example, then we'd need to go render all the rows to the new wchan column
width...

It's simpler to just redraw it all if anything has changed,  and this stuff
doesn't generally change that frequently in practice so it's pretty effective
as-is.

1 files changed, 44 insertions, 9 deletions

diff --git a/src/overlay.c b/src/overlay.c
index 25d6edf..06d2de2 100644
--- a/src/overlay.c
+++ b/src/overlay.c
@@ -238,6 +238,27 @@ static int count_rows(vmon_proc_t *proc) {
 	return count;
 }
 
+
+/* helper for detecting if any children/threads in the process heirarchy rooted @ proc are new/stale this sample */
+static int proc_heirarchy_changed(vmon_proc_t *proc) {
+	vmon_proc_t	*child;
+
+	if (proc->children_changed || proc->threads_changed) return 1;
+
+	if (!proc->is_thread) {
+		list_for_each_entry(child, &proc->threads, threads) {
+			if (proc_heirarchy_changed(child)) return 1;
+		}
+	}
+
+	list_for_each_entry(child, &proc->children, siblings) {
+		if (proc_heirarchy_changed(child)) return 1;
+	}
+
+	return 0;
+}
+
+
 /* helper for drawing the vertical bars in the graph layers */
 static void draw_bars(vwm_t *vwm, vwm_xwindow_t *xwin, int row, double a_fraction, double a_total, double b_fraction, double b_total)
 {
@@ -263,7 +284,7 @@ static void draw_bars(vwm_t *vwm, vwm_xwindow_t *xwin, int row, double a_fractio
 
 
 /* draws proc in a row of the process heirarchy */
-static void draw_heirarchy_row(vwm_t *vwm, vwm_xwindow_t *xwin, vmon_proc_t *proc, int depth, int row)
+static void draw_heirarchy_row(vwm_t *vwm, vwm_xwindow_t *xwin, vmon_proc_t *proc, int depth, int row, int heirarchy_changed)
 {
 	vmon_proc_stat_t	*proc_stat = proc->stores[VMON_STORE_PROC_STAT];
 	vmon_proc_t		*child;
@@ -273,7 +294,15 @@ static void draw_heirarchy_row(vwm_t *vwm, vwm_xwindow_t *xwin, vmon_proc_t *pro
 	int			nr_items;
 
 /* process heirarchy text and accompanying per-process details like wchan/pid/state... */
-	/* this stuff can be skipped when monitors aren't visible */
+
+	/* skip if obviously unnecessary (this can be further improved, but this makes a big difference as-is) */
+	if (!xwin->overlay.redraw_needed &&
+	    !heirarchy_changed &&
+	    !BITTEST(proc_stat->changed, VMON_PROC_STAT_WCHAN) &&
+	    !BITTEST(proc_stat->changed, VMON_PROC_STAT_PID) &&
+	    !BITTEST(proc_stat->changed, VMON_PROC_STAT_STATE) &&
+	    !BITTEST(proc_stat->changed, VMON_PROC_STAT_ARGV)) return;
+
 	/* TODO: make the columns interactively configurable @ runtime */
 	if (!proc->is_new) {
 	/* XXX for now always clear the row, this should be capable of being optimized in the future (if the datums driving the text haven't changed...) */
@@ -399,12 +428,13 @@ static void draw_heirarchy_row(vwm_t *vwm, vwm_xwindow_t *xwin, vmon_proc_t *pro
 			}
 		}
 	}
+
 	shadow_row(vwm, xwin, row);
 }
 
 
 /* recursive draw function for "rest" of overlay: the per-process rows (heirarchy, argv, state, wchan, pid...) */
-static void draw_overlay_rest(vwm_t *vwm, vwm_xwindow_t *xwin, vmon_proc_t *proc, int *depth, int *row)
+static void draw_overlay_rest(vwm_t *vwm, vwm_xwindow_t *xwin, vmon_proc_t *proc, int *depth, int *row, int heirarchy_changed)
 {
 	vmon_proc_t		*child;
 	vwm_perproc_ctxt_t	*proc_ctxt = proc->foo;
@@ -439,13 +469,13 @@ static void draw_overlay_rest(vwm_t *vwm, vwm_xwindow_t *xwin, vmon_proc_t *proc
 
 		(*depth)++;
 		list_for_each_entry_prev(child, &proc->children, siblings) {
-			draw_overlay_rest(vwm, xwin, child, depth, row);
+			draw_overlay_rest(vwm, xwin, child, depth, row, heirarchy_changed);
 			(*row)--;
 		}
 
 		if (!proc->is_thread) {
 			list_for_each_entry_prev(child, &proc->threads, threads) {
-				draw_overlay_rest(vwm, xwin, child, depth, row);
+				draw_overlay_rest(vwm, xwin, child, depth, row, heirarchy_changed);
 				(*row)--;
 			}
 		}
@@ -524,7 +554,7 @@ static void draw_overlay_rest(vwm_t *vwm, vwm_xwindow_t *xwin, vmon_proc_t *proc
 
 	draw_bars(vwm, xwin, *row, stime_delta, total_delta, utime_delta, total_delta);
 
-	draw_heirarchy_row(vwm, xwin, proc, *depth, *row);
+	draw_heirarchy_row(vwm, xwin, proc, *depth, *row, heirarchy_changed);
 
 	(*row)++;
 
@@ -532,12 +562,12 @@ static void draw_overlay_rest(vwm_t *vwm, vwm_xwindow_t *xwin, vmon_proc_t *proc
 	(*depth)++;
 	if (!proc->is_thread) {	/* XXX: the threads member serves as the list head only when not a thread */
 		list_for_each_entry(child, &proc->threads, threads) {
-			draw_overlay_rest(vwm, xwin, child, depth, row);
+			draw_overlay_rest(vwm, xwin, child, depth, row, heirarchy_changed);
 		}
 	}
 
 	list_for_each_entry(child, &proc->children, siblings) {
-		draw_overlay_rest(vwm, xwin, child, depth, row);
+		draw_overlay_rest(vwm, xwin, child, depth, row, heirarchy_changed);
 	}
 	(*depth)--;
 }
@@ -555,6 +585,8 @@ static void draw_overlay(vwm_t *vwm, vwm_xwindow_t *xwin, vmon_proc_t *proc, int
 	char			str[256];
 	int			str_len, str_width;
 
+	int			heirarchy_changed = 0;
+
 /* CPU utilization graphs */
 	/* IOWait and Idle % @ row 0 */
 	draw_bars(vwm, xwin, *row, iowait_delta, total_delta, idle_delta, total_delta);
@@ -573,7 +605,10 @@ static void draw_overlay(vwm_t *vwm, vwm_xwindow_t *xwin, vmon_proc_t *proc, int
 	}
 	(*row)++;
 
-	draw_overlay_rest(vwm, xwin, proc, depth, row);
+	if (!xwin->overlay.redraw_needed) heirarchy_changed = proc_heirarchy_changed(proc);
+
+
+	draw_overlay_rest(vwm, xwin, proc, depth, row, heirarchy_changed);
 
 	xwin->overlay.redraw_needed = 0;