if (tp->snd_cwnd < tp->snd_ssthresh) { 
if (tp->snd_cwnd <= tp->snd_ssthresh) { 
static void tcp_vegas_cong_avoid(struct sock *sk, u32 ack,				 u32 seq_rtt, u32 in_flight, int flag){	struct tcp_sock *tp = tcp_sk(sk);	struct vegas *vegas = inet_csk_ca(sk);	if (!vegas->doing_vegas_now)		return tcp_reno_cong_avoid(sk, ack, seq_rtt, in_flight, flag);	/* 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;		/* Take into account the current RTT sample too, to		 * decrease the impact of delayed acks. This double counts		 * this sample since we count it for the next window as well,		 * but that's not too awful, since we're taking the min,		 * rather than averaging.		 */		tcp_vegas_rtt_calc(sk, seq_rtt * 1000);		/* We do the Vegas calculations only if we got enough RTT		 * samples that we can be reasonably sure that we got		 * at least one RTT sample that wasn't from a delayed ACK.		 * If we only had 2 samples total,		 * then that means we're getting only 1 ACK per RTT, which		 * means they're almost certainly delayed ACKs.		 * If  we have 3 samples, we should be OK.		 */		if (vegas->cntRTT <= 2) {			/* We don't have enough RTT samples to do the Vegas			 * calculation, so we'll behave like Reno.			 */			if (tp->snd_cwnd > tp->snd_ssthresh)				tp->snd_cwnd++;		} else {			u32 rtt, target_cwnd, diff;			/* We have enough RTT samples, so, using the Vegas			 * algorithm, we determine if we should increase or			 * decrease cwnd, and by how much.			 */			/* Pluck out the RTT we are using for the Vegas			 * calculations. This is the min RTT seen during the			 * last RTT. Taking the min filters out the effects			 * of delayed ACKs, at the cost of noticing congestion			 * a bit later.			 */			rtt = vegas->minRTT;			/* Calculate the cwnd we should have, if we weren't			 * going too fast.			 *			 * 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 = ((old_wnd * vegas->baseRTT)				       << V_PARAM_SHIFT) / 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;			if (tp->snd_cwnd < tp->snd_ssthresh) {				/* Slow start.  */				if (diff > gamma) {					/* Going too fast. Time to slow down					 * and switch to congestion avoidance.					 */					tp->snd_ssthresh = 2;					/* Set cwnd to match the actual rate					 * exactly:					 *   cwnd = (actual rate) * baseRTT					 * Then we add 1 because the integer					 * truncation robs us of full link					 * utilization.					 */					tp->snd_cwnd = min(tp->snd_cwnd,							   (target_cwnd >>							    V_PARAM_SHIFT)+1);				}			} else {				/* Congestion avoidance. */				u32 next_snd_cwnd;				/* Figure out where we would like cwnd				 * to be.				 */				if (diff > beta) {					/* The old window was too fast, so					 * we slow down.					 */					next_snd_cwnd = old_snd_cwnd - 1;				} else if (diff < alpha) {					/* We don't have enough extra packets					 * in the network, so speed up.					 */					next_snd_cwnd = old_snd_cwnd + 1;				} 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--;			}		}		/* Wipe the slate clean for the next RTT. */		vegas->cntRTT = 0;		vegas->minRTT = 0x7fffffff;	}	/* The following code is executed for every ack we receive,	 * except for conditions checked in should_advance_cwnd()	 * before the call to tcp_cong_avoid(). Mainly this means that	 * we only execute this code if the ack actually acked some	 * data.	 */	/* If we are in slow start, increase our cwnd in response to this ACK.	 * (If we are not in slow start then we are in congestion avoidance,	 * and adjust our congestion window only once per RTT. See the code	 * above.)	 */	if (tp->snd_cwnd <= tp->snd_ssthresh)		tp->snd_cwnd++;	/* to keep cwnd from growing without bound */	tp->snd_cwnd = min_t(u32, tp->snd_cwnd, tp->snd_cwnd_clamp);	/* Make sure that we are never so timid as to reduce our cwnd below	 * 2 MSS.	 *	 * Going below 2 MSS would risk huge delayed ACKs from our receiver.	 */	tp->snd_cwnd = max(tp->snd_cwnd, 2U);}
4520	/local/tlutelli/issta_data/temp/c/2005_temp/2005/4520/7faffa1c7fb9b8e8917e3225d4e2638270c0a48b/tcp_vegas.c/buggy/net/ipv4/tcp_vegas.c