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

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

Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Stephen Hemminger
2007-05-17 00:04:18 -07:00
committed by David S. Miller
parent 4ce61d1c7a
commit a02ba04166
1 changed files with 21 additions and 17 deletions
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28
net/ipv4/tcp_cong.c
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@@ -276,30 +276,34 @@ int tcp_set_congestion_control(struct sock *sk, const char *name)
/* /*
* Slow start (exponential increase) with * Slow start is used when congestion window is less than slow start
* RFC3742 Limited Slow Start (fast linear increase) support. * 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) void tcp_slow_start(struct tcp_sock *tp)
{ {
int cnt = 0; int cnt; /* increase in packets */
if (sysctl_tcp_abc) { /* RFC3465: ABC Slow start
/* RFC3465: Slow Start * Increase only after a full MSS of bytes is acked
*
* TCP sender SHOULD increase cwnd by the number of * TCP sender SHOULD increase cwnd by the number of
* previously unacknowledged bytes ACKed by each incoming * previously unacknowledged bytes ACKed by each incoming
* acknowledgment, provided the increase is not more than L * 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; return;
}
if (sysctl_tcp_max_ssthresh > 0 && if (sysctl_tcp_max_ssthresh > 0 && tp->snd_cwnd > sysctl_tcp_max_ssthresh)
tp->snd_cwnd > sysctl_tcp_max_ssthresh) cnt = sysctl_tcp_max_ssthresh >> 1; /* limited slow start */
cnt += sysctl_tcp_max_ssthresh>>1;
else 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) if (sysctl_tcp_abc > 1 && tp->bytes_acked >= 2*tp->mss_cache)
cnt <<= 1; cnt <<= 1;
tp->bytes_acked = 0; tp->bytes_acked = 0;