[TCP] slow start: Make comments and code logic clearer.
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>
diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c
index 86b2653..1260e52 100644
--- a/net/ipv4/tcp_cong.c
+++ b/net/ipv4/tcp_cong.c
@@ -276,30 +276,34 @@
/*
- * 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
- * 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;
- }
+ /* 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;