Commit 9dc27415 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller

tcp: fix ABC in tcp_slow_start()

When/if sysctl_tcp_abc > 1, we expect to increase cwnd by 2 if the
received ACK acknowledges more than 2*MSS bytes, in tcp_slow_start()

Problem is this RFC 3465 statement is not correctly coded, as
the while () loop increases snd_cwnd one by one.

Add a new variable to avoid this off-by one error.
Signed-off-by: default avatarEric Dumazet <edumazet@google.com>
Cc: Tom Herbert <therbert@google.com>
Cc: Yuchung Cheng <ycheng@google.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Nandita Dukkipati <nanditad@google.com>
Cc: John Heffner <johnwheffner@gmail.com>
Cc: Stephen Hemminger <shemminger@vyatta.com>
Acked-by: default avatarYuchung Cheng <ycheng@google.com>
Acked-by: default avatarNeal Cardwell <ncardwell@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 5815d5e7
...@@ -307,6 +307,7 @@ EXPORT_SYMBOL_GPL(tcp_is_cwnd_limited); ...@@ -307,6 +307,7 @@ EXPORT_SYMBOL_GPL(tcp_is_cwnd_limited);
void tcp_slow_start(struct tcp_sock *tp) void tcp_slow_start(struct tcp_sock *tp)
{ {
int cnt; /* increase in packets */ int cnt; /* increase in packets */
unsigned int delta = 0;
/* RFC3465: ABC Slow start /* RFC3465: ABC Slow start
* Increase only after a full MSS of bytes is acked * Increase only after a full MSS of bytes is acked
...@@ -333,9 +334,9 @@ void tcp_slow_start(struct tcp_sock *tp) ...@@ -333,9 +334,9 @@ void tcp_slow_start(struct tcp_sock *tp)
tp->snd_cwnd_cnt += cnt; tp->snd_cwnd_cnt += cnt;
while (tp->snd_cwnd_cnt >= tp->snd_cwnd) { while (tp->snd_cwnd_cnt >= tp->snd_cwnd) {
tp->snd_cwnd_cnt -= tp->snd_cwnd; tp->snd_cwnd_cnt -= tp->snd_cwnd;
if (tp->snd_cwnd < tp->snd_cwnd_clamp) delta++;
tp->snd_cwnd++;
} }
tp->snd_cwnd = min(tp->snd_cwnd + delta, tp->snd_cwnd_clamp);
} }
EXPORT_SYMBOL_GPL(tcp_slow_start); EXPORT_SYMBOL_GPL(tcp_slow_start);
......
Markdown is supported
0%
or
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment