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Date: Fri, 20 Jul 2012 17:02:33 +0200 From: Eric Dumazet <eric.dumazet@...il.com> To: David Miller <davem@...emloft.net> Cc: netdev <netdev@...r.kernel.org>, Tom Herbert <therbert@...gle.com>, Neal Cardwell <ncardwell@...gle.com>, Yuchung Cheng <ycheng@...gle.com>, Stephen Hemminger <shemminger@...tta.com>, John Heffner <johnwheffner@...il.com>, Nandita Dukkipati <nanditad@...gle.com> Subject: [PATCH v2 net-next] tcp: fix ABC in tcp_slow_start() From: Eric Dumazet <edumazet@...gle.com> 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: Eric Dumazet <edumazet@...gle.com> Cc: Tom Herbert <therbert@...gle.com> Cc: Yuchung Cheng <ycheng@...gle.com> Cc: Neal Cardwell <ncardwell@...gle.com> Cc: Nandita Dukkipati <nanditad@...gle.com> Cc: John Heffner <johnwheffner@...il.com> Cc: Stephen Hemminger <shemminger@...tta.com> --- v2: added John suggestion net/ipv4/tcp_cong.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-) diff --git a/net/ipv4/tcp_cong.c b/net/ipv4/tcp_cong.c index 04dbd7a..4d4db16 100644 --- a/net/ipv4/tcp_cong.c +++ b/net/ipv4/tcp_cong.c @@ -307,6 +307,7 @@ EXPORT_SYMBOL_GPL(tcp_is_cwnd_limited); void tcp_slow_start(struct tcp_sock *tp) { int cnt; /* increase in packets */ + unsigned int delta = 0; /* RFC3465: ABC Slow start * Increase only after a full MSS of bytes is acked @@ -333,9 +334,9 @@ void tcp_slow_start(struct tcp_sock *tp) tp->snd_cwnd_cnt += cnt; while (tp->snd_cwnd_cnt >= tp->snd_cwnd) { tp->snd_cwnd_cnt -= tp->snd_cwnd; - if (tp->snd_cwnd < tp->snd_cwnd_clamp) - tp->snd_cwnd++; + delta++; } + tp->snd_cwnd = min(tp->snd_cwnd + delta, tp->snd_cwnd_clamp); } EXPORT_SYMBOL_GPL(tcp_slow_start); -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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