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sctp: update order of adjustments of partial_bytes_acked and cwnd 

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>
This commit is contained in:
Marcelo Ricardo Leitner 2017-06-23 19:59:33 -03:00 committed by David S. Miller
parent f3ecab3824
commit d0b53f4097
1 changed files with 8 additions and 7 deletions
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15
net/sctp/transport.c
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@ -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, "