sctp: update order of adjustments of partial_bytes_acked and cwnd (d0b53f40) · Commits · 戴 / test

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.leitner@gmail.com> Signed-off-by:

David S. Miller <davem@davemloft.net>

net/sctp/transport.c

+8 −7

Original line number	Diff line number	Diff line
		@@ -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, "

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