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
......@@ -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;
if (sysctl_tcp_abc) {
/* RFC3465: Slow Start
* 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)
return;
}
int cnt; /* increase in packets */
/* 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 (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;
......
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