The TCP PAWS fix for kernels with fast tick rates (r231767) changed the TCP

timestamp related stack variables to reference ms directly instead of ticks.
The h_ertt(4) Khelp module relies on TCP timestamp information in order to
calculate its enhanced RTT estimates, but was not updated as part of r231767.

Consequently, h_ertt has not been calculating correct RTT estimates since
r231767 was comitted, which in turn broke all delay-based congestion control
algorithms because they rely on the h_ertt RTT estimates.

Fix the breakage by switching h_ertt to use tcp_ts_getticks() in place of all
previous uses of the ticks variable. This ensures all timestamp related
variables in h_ertt use the same units as the TCP stack and therefore results in
meaningful comparisons and RTT estimate calculations.

Reported & tested by:	Naeem Khademi (naeemk at ifi uio no)
Discussed with:	bz
MFC after:	3 days

1 files changed, 6 insertions, 4 deletions

diff --git a/sys/netinet/khelp/h_ertt.c b/sys/netinet/khelp/h_ertt.c
index 7ce195c..13d15e0 100644
--- a/sys/netinet/khelp/h_ertt.c
+++ b/sys/netinet/khelp/h_ertt.c
@@ -151,11 +151,13 @@ marked_packet_rtt(struct txseginfo *txsi, struct ertt *e_t, struct tcpcb *tp,
 		*prtt_bytes_adjust += *pmeasurenext_len;
 	} else {
 		if (mflag & FORCED_MEASUREMENT) {
-			e_t->markedpkt_rtt = ticks - *pmeasurenext + 1;
+			e_t->markedpkt_rtt = tcp_ts_getticks() -
+			    *pmeasurenext + 1;
 			e_t->bytes_tx_in_marked_rtt = e_t->bytes_tx_in_rtt +
 			    *pmeasurenext_len - *prtt_bytes_adjust;
 		} else {
-			e_t->markedpkt_rtt = ticks - txsi->tx_ts + 1;
+			e_t->markedpkt_rtt = tcp_ts_getticks() -
+			    txsi->tx_ts + 1;
 			e_t->bytes_tx_in_marked_rtt = e_t->bytes_tx_in_rtt -
 			    *prtt_bytes_adjust;
 		}
@@ -349,7 +351,7 @@ ertt_packet_measurement_hook(int hhook_type, int hhook_id, void *udata,
 			 */
 			if (!e_t->dlyack_rx || multiack || new_sacked_bytes) {
 				/* Make an accurate new measurement. */
-				e_t->rtt = ticks - txsi->tx_ts + 1;
+				e_t->rtt = tcp_ts_getticks() - txsi->tx_ts + 1;
 
 				if (e_t->rtt < e_t->minrtt || e_t->minrtt == 0)
 					e_t->minrtt = e_t->rtt;
@@ -477,7 +479,7 @@ ertt_add_tx_segment_info_hook(int hhook_type, int hhook_id, void *udata,
 				    tp->ts_offset;
 				txsi->rx_ts = ntohl(to->to_tsecr);
 			} else {
-				txsi->tx_ts = ticks;
+				txsi->tx_ts = tcp_ts_getticks();
 				txsi->rx_ts = 0; /* No received time stamp. */
 			}
 			TAILQ_INSERT_TAIL(&e_t->txsegi_q, txsi, txsegi_lnk);