diff --git a/drivers/md/md.c b/drivers/md/md.c
index f3fed662f32e..78c7418478d6 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -3846,11 +3846,20 @@ static int is_mddev_idle(mddev_t *mddev)
 		curr_events = disk_stat_read(disk, sectors[0]) + 
 				disk_stat_read(disk, sectors[1]) - 
 				atomic_read(&disk->sync_io);
-		/* Allow some slack between valud of curr_events and last_events,
-		 * as there are some uninteresting races.
+		/* The difference between curr_events and last_events
+		 * will be affected by any new non-sync IO (making
+		 * curr_events bigger) and any difference in the amount of
+		 * in-flight syncio (making current_events bigger or smaller)
+		 * The amount in-flight is currently limited to
+		 * 32*64K in raid1/10 and 256*PAGE_SIZE in raid5/6
+		 * which is at most 4096 sectors.
+		 * These numbers are fairly fragile and should be made
+		 * more robust, probably by enforcing the
+		 * 'window size' that md_do_sync sort-of uses.
+		 *
 		 * Note: the following is an unsigned comparison.
 		 */
-		if ((curr_events - rdev->last_events + 32) > 64) {
+		if ((curr_events - rdev->last_events + 4096) > 8192) {
 			rdev->last_events = curr_events;
 			idle = 0;
 		}
@@ -4109,7 +4118,7 @@ static void md_do_sync(mddev_t *mddev)
 		if (currspeed > sysctl_speed_limit_min) {
 			if ((currspeed > sysctl_speed_limit_max) ||
 					!is_mddev_idle(mddev)) {
-				msleep(250);
+				msleep(500);
 				goto repeat;
 			}
 		}