From: Simon Wilkinson Date: Fri, 17 Jun 2011 18:38:29 +0000 (+0100) Subject: rx: Account for delayed ACKS when computing RTO X-Git-Tag: openafs-devel-1_7_1~374 X-Git-Url: https://git.openafs.org/?p=openafs.git;a=commitdiff_plain;h=699330682f3cb001bf1bfbeaffd806600ccf69e8 rx: Account for delayed ACKS when computing RTO RX currently only soft ACKs every second packet, therefore a soft ACK may be delayed by a period of time (currently 100ms, although RX did expose this as a public variable in earlier versions). RTT values are computed using only non-delayed ACKs, so the timeout is a smoothed average of the exact time taken to send and directly ACK a packet. Therefore, if the peer ends up using a delayed ACK for the packet, using just the RTT will cause that packet to be timed out. A while ago, this was dealt with by padding the calculated RTT with an additional 350ms. This was then removed, and changed to a 350ms minimum value. When this caused large numbers of spurious resends, the padding was restored, but with a 20ms default value. As noted above, 20ms is too low, as we may wait for up to 100ms before sending an ACK. This patch changes minPeerTimeout so that it does what it says on the tin - sets a minimum value below which the peer timout may not fall. It then adds to either this value, or the calculated one, 200ms of padding. This makes our padding identical to TCPs, and allows some future leway as to the softAckDelay value. Change-Id: I48ab28e03bb7c0a49fe21c21f83adbb02b7665f2 Reviewed-on: http://gerrit.openafs.org/4859 Reviewed-by: Derrick Brashear Tested-by: BuildBot --- diff --git a/src/rx/rx.c b/src/rx/rx.c index 26c0aef..fa1ba86 100644 --- a/src/rx/rx.c +++ b/src/rx/rx.c @@ -6818,11 +6818,16 @@ rxi_ComputeRoundTripTime(struct rx_packet *p, peer->rtt = _8THMSEC(&thisRtt) + 8; peer->rtt_dev = peer->rtt >> 2; /* rtt/2: they're scaled differently */ } - /* the timeout is RTT + 4*MDEV + rx_minPeerTimeout msec. - * This is because one end or the other of these connections is usually - * in a user process, and can be switched and/or swapped out. So on fast, - * reliable networks, the timeout would otherwise be too short. */ - rtt_timeout = ((peer->rtt >> 3) + peer->rtt_dev) + rx_minPeerTimeout; + /* the smoothed RTT time is RTT + 4*MDEV + * + * We allow a user specified minimum to be set for this, to allow clamping + * at a minimum value in the same way as TCP. In addition, we have to allow + * for the possibility that this packet is answered by a delayed ACK, so we + * add on a fixed 200ms to account for that timer expiring. + */ + + rtt_timeout = MAX(((peer->rtt >> 3) + peer->rtt_dev), + rx_minPeerTimeout) + 200; clock_Zero(&(peer->timeout)); clock_Addmsec(&(peer->timeout), rtt_timeout);