RFC4960 Errata 3.12 says RFC4960 is unclear about the order of adjustments applied to partial_bytes_acked and cwnd in the congestion avoidance phase, and that the actual order should be: partial_bytes_acked is reset to (partial_bytes_acked - cwnd). Next, cwnd is increased by MTU.
We were first increasing cwnd, and then subtracting the new value pba, which leads to a different result as pba is smaller than what it should and could cause cwnd to not grow as much. See-also: https://tools.ietf.org/html/draft-ietf-tsvwg-rfc4960-errata-01#section-3.12 Signed-off-by: Marcelo Ricardo Leitner <marcelo.leit...@gmail.com> --- net/sctp/transport.c | 15 ++++++++------- 1 file changed, 8 insertions(+), 7 deletions(-) diff --git a/net/sctp/transport.c b/net/sctp/transport.c index 721eeebfcd8a50609877db61ede41575e012606a..04b6dd1a07ded25fe5874518b0944a6d9df4099b 100644 --- a/net/sctp/transport.c +++ b/net/sctp/transport.c @@ -452,17 +452,18 @@ void sctp_transport_raise_cwnd(struct sctp_transport *transport, * chunks acknowledged by the new Cumulative TSN Ack and by * Gap Ack Blocks. * - * When partial_bytes_acked is equal to or greater than cwnd - * and before the arrival of the SACK the sender had cwnd or - * more bytes of data outstanding (i.e., before arrival of the - * SACK, flightsize was greater than or equal to cwnd), - * increase cwnd by MTU, and reset partial_bytes_acked to - * (partial_bytes_acked - cwnd). + * When partial_bytes_acked is equal to or greater than + * cwnd and before the arrival of the SACK the sender + * had cwnd or more bytes of data outstanding (i.e., + * before arrival of the SACK, flightsize was greater + * than or equal to cwnd), partial_bytes_acked is reset + * to (partial_bytes_acked - cwnd). Next, cwnd is + * increased by MTU. (RFC 4960 Errata 3.12) */ pba += bytes_acked; if (pba >= cwnd) { + pba = pba - cwnd; cwnd += pmtu; - pba = ((cwnd < pba) ? (pba - cwnd) : 0); } pr_debug("%s: congestion avoidance: transport:%p, " -- 2.9.4
