lguest: update commentry

[linux-2.6-omap-h63xx.git] / Documentation / lguest / lguest.c

diff --git a/Documentation/lguest/lguest.c b/Documentation/lguest/lguest.c
index 655414821edc361fae2382104a068bb2c895f0de..7228369d1014b956ff3c8843d8ef642a225682b3 100644 (file)
--- a/Documentation/lguest/lguest.c
+++ b/Documentation/lguest/lguest.c
@@ -895,6 +895,9 @@ static void handle_console_output(int fd, struct virtqueue *vq, bool timeout)
        }
 }
 
+/* This is called when we no longer want to hear about Guest changes to a
+ * virtqueue.  This is more efficient in high-traffic cases, but it means we
+ * have to set a timer to check if any more changes have occurred. */
 static void block_vq(struct virtqueue *vq)
 {
        struct itimerval itm;
@@ -939,6 +942,11 @@ static void handle_net_output(int fd, struct virtqueue *vq, bool timeout)
        if (!timeout && num)
                block_vq(vq);
 
+       /* We never quite know how long should we wait before we check the
+        * queue again for more packets.  We start at 500 microseconds, and if
+        * we get fewer packets than last time, we assume we made the timeout
+        * too small and increase it by 10 microseconds.  Otherwise, we drop it
+        * by one microsecond every time.  It seems to work well enough. */
        if (timeout) {
                if (num < last_timeout_num)
                        timeout_usec += 10;