Commit a02ba041 authored by Stephen Hemminger's avatar Stephen Hemminger Committed by David S. Miller
Browse files

[TCP] slow start: Make comments and code logic clearer. 



Add more comments to describe our version of tcp_slow_start().

Signed-off-by: default avatarStephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 4ce61d1c

net/ipv4/tcp_cong.c

+22 −18
Original line number Diff line number Diff line
@@ -276,30 +276,34 @@ int tcp_set_congestion_control(struct sock *sk, const char *name) 




/*

 * Slow start (exponential increase) with

 * RFC3742 Limited Slow Start (fast linear increase) support.

 * Slow start is used when congestion window is less than slow start

 * threshold. This version implements the basic RFC2581 version

 * and optionally supports:

 * 	RFC3742 Limited Slow Start  	  - growth limited to max_ssthresh

 *	RFC3465 Appropriate Byte Counting - growth limited by bytes acknowledged

 */

void tcp_slow_start(struct tcp_sock *tp)

{

	int cnt = 0;

	int cnt; /* increase in packets */



	if (sysctl_tcp_abc) {

		/* RFC3465: Slow Start

	/* RFC3465: ABC Slow start

	 * Increase only after a full MSS of bytes is acked

	 *

	 * TCP sender SHOULD increase cwnd by the number of

	 * previously unacknowledged bytes ACKed by each incoming

	 * acknowledgment, provided the increase is not more than L

	 */

		if (tp->bytes_acked < tp->mss_cache)

	if (sysctl_tcp_abc && tp->bytes_acked < tp->mss_cache)

		return;

	}



	if (sysctl_tcp_max_ssthresh > 0 &&

	    tp->snd_cwnd > sysctl_tcp_max_ssthresh)

		cnt += sysctl_tcp_max_ssthresh>>1;

	if (sysctl_tcp_max_ssthresh > 0 && tp->snd_cwnd > sysctl_tcp_max_ssthresh)

		cnt = sysctl_tcp_max_ssthresh >> 1;	/* limited slow start */

	else

		cnt += tp->snd_cwnd;

		cnt = tp->snd_cwnd;			/* exponential increase */



	/* RFC3465: We MAY increase by 2 if discovered delayed ack */

	/* RFC3465: ABC

	 * We MAY increase by 2 if discovered delayed ack

	 */

	if (sysctl_tcp_abc > 1 && tp->bytes_acked >= 2*tp->mss_cache)

		cnt <<= 1;

	tp->bytes_acked = 0;