---

yaml
---
r: 119881
b: refs/heads/master
c: 8d3a564
h: refs/heads/master
i:
  119879: eee6f80
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 8c83f80b2d335176f72d8729fe1dfe19c5812cb1
+refs/heads/master: 8d3a564da34e5844aca4f991b73f8ca512246b23

trunk/net/ipv4/tcp_vegas.c

@@ -40,18 +40,14 @@
 
 #include "tcp_vegas.h"
 
-/* Default values of the Vegas variables, in fixed-point representation
- * with V_PARAM_SHIFT bits to the right of the binary point.
- */
-#define V_PARAM_SHIFT 1
-static int alpha = 2<<V_PARAM_SHIFT;
-static int beta  = 4<<V_PARAM_SHIFT;
-static int gamma = 1<<V_PARAM_SHIFT;
+static int alpha = 2;
+static int beta  = 4;
+static int gamma = 1;
 
 module_param(alpha, int, 0644);
-MODULE_PARM_DESC(alpha, "lower bound of packets in network (scale by 2)");
+MODULE_PARM_DESC(alpha, "lower bound of packets in network");
 module_param(beta, int, 0644);
-MODULE_PARM_DESC(beta, "upper bound of packets in network (scale by 2)");
+MODULE_PARM_DESC(beta, "upper bound of packets in network");
 module_param(gamma, int, 0644);
 MODULE_PARM_DESC(gamma, "limit on increase (scale by 2)");
 
@@ -172,49 +168,13 @@ static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
 		return;
 	}
 
-	/* The key players are v_beg_snd_una and v_beg_snd_nxt.
-	 *
-	 * These are so named because they represent the approximate values
-	 * of snd_una and snd_nxt at the beginning of the current RTT. More
-	 * precisely, they represent the amount of data sent during the RTT.
-	 * At the end of the RTT, when we receive an ACK for v_beg_snd_nxt,
-	 * we will calculate that (v_beg_snd_nxt - v_beg_snd_una) outstanding
-	 * bytes of data have been ACKed during the course of the RTT, giving
-	 * an "actual" rate of:
-	 *
-	 *     (v_beg_snd_nxt - v_beg_snd_una) / (rtt duration)
-	 *
-	 * Unfortunately, v_beg_snd_una is not exactly equal to snd_una,
-	 * because delayed ACKs can cover more than one segment, so they
-	 * don't line up nicely with the boundaries of RTTs.
-	 *
-	 * Another unfortunate fact of life is that delayed ACKs delay the
-	 * advance of the left edge of our send window, so that the number
-	 * of bytes we send in an RTT is often less than our cwnd will allow.
-	 * So we keep track of our cwnd separately, in v_beg_snd_cwnd.
-	 */
-
 	if (after(ack, vegas->beg_snd_nxt)) {
 		/* Do the Vegas once-per-RTT cwnd adjustment. */
-		u32 old_wnd, old_snd_cwnd;
-
-
-		/* Here old_wnd is essentially the window of data that was
-		 * sent during the previous RTT, and has all
-		 * been acknowledged in the course of the RTT that ended
-		 * with the ACK we just received. Likewise, old_snd_cwnd
-		 * is the cwnd during the previous RTT.
-		 */
-		old_wnd = (vegas->beg_snd_nxt - vegas->beg_snd_una) /
-			tp->mss_cache;
-		old_snd_cwnd = vegas->beg_snd_cwnd;
 
 		/* Save the extent of the current window so we can use this
 		 * at the end of the next RTT.
 		 */
-		vegas->beg_snd_una  = vegas->beg_snd_nxt;
 		vegas->beg_snd_nxt  = tp->snd_nxt;
-		vegas->beg_snd_cwnd = tp->snd_cwnd;
 
 		/* We do the Vegas calculations only if we got enough RTT
 		 * samples that we can be reasonably sure that we got
@@ -252,22 +212,14 @@ static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
 			 *
 			 * This is:
 			 *     (actual rate in segments) * baseRTT
-			 * We keep it as a fixed point number with
-			 * V_PARAM_SHIFT bits to the right of the binary point.
 			 */
-			target_cwnd = ((u64)old_wnd * vegas->baseRTT);
-			target_cwnd <<= V_PARAM_SHIFT;
-			do_div(target_cwnd, rtt);
+			target_cwnd = tp->snd_cwnd * vegas->baseRTT / rtt;
 
 			/* Calculate the difference between the window we had,
 			 * and the window we would like to have. This quantity
 			 * is the "Diff" from the Arizona Vegas papers.
-			 *
-			 * Again, this is a fixed point number with
-			 * V_PARAM_SHIFT bits to the right of the binary
-			 * point.
 			 */
-			diff = (old_wnd << V_PARAM_SHIFT) - target_cwnd;
+			diff = tp->snd_cwnd * (rtt-vegas->baseRTT) / vegas->baseRTT;
 
 			if (diff > gamma && tp->snd_ssthresh > 2 ) {
 				/* Going too fast. Time to slow down
@@ -282,16 +234,13 @@ static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
 				 * truncation robs us of full link
 				 * utilization.
 				 */
-				tp->snd_cwnd = min(tp->snd_cwnd,
-						   ((u32)target_cwnd >>
-						    V_PARAM_SHIFT)+1);
+				tp->snd_cwnd = min(tp->snd_cwnd, (u32)target_cwnd+1);
 
 			} else if (tp->snd_cwnd <= tp->snd_ssthresh) {
 				/* Slow start.  */
 				tcp_slow_start(tp);
 			} else {
 				/* Congestion avoidance. */
-				u32 next_snd_cwnd;
 
 				/* Figure out where we would like cwnd
 				 * to be.
@@ -300,26 +249,17 @@ static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack, u32 in_flight)
 					/* The old window was too fast, so
 					 * we slow down.
 					 */
-					next_snd_cwnd = old_snd_cwnd - 1;
+					tp->snd_cwnd--;
 				} else if (diff < alpha) {
 					/* We don't have enough extra packets
 					 * in the network, so speed up.
 					 */
-					next_snd_cwnd = old_snd_cwnd + 1;
+					tp->snd_cwnd++;
 				} else {
 					/* Sending just as fast as we
 					 * should be.
 					 */
-					next_snd_cwnd = old_snd_cwnd;
 				}
-
-				/* Adjust cwnd upward or downward, toward the
-				 * desired value.
-				 */
-				if (next_snd_cwnd > tp->snd_cwnd)
-					tp->snd_cwnd++;
-				else if (next_snd_cwnd < tp->snd_cwnd)
-					tp->snd_cwnd--;
 			}
 
 			if (tp->snd_cwnd < 2)