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-rw-r--r--src/vnet/tcp/tcp_input.c43
1 files changed, 21 insertions, 22 deletions
diff --git a/src/vnet/tcp/tcp_input.c b/src/vnet/tcp/tcp_input.c
index 519219e2c74..5fa7bf23c72 100644
--- a/src/vnet/tcp/tcp_input.c
+++ b/src/vnet/tcp/tcp_input.c
@@ -424,31 +424,26 @@ acceptable:
/**
* Compute smoothed RTT as per VJ's '88 SIGCOMM and RFC6298
*
- * Note that although the original article, srtt and rttvar are scaled
+ * Note that although in the original article srtt and rttvar are scaled
* to minimize round-off errors, here we don't. Instead, we rely on
* better precision time measurements.
+ *
+ * A known limitation of the algorithm is that a drop in rtt results in a
+ * rttvar increase and bigger RTO.
+ *
+ * mrtt must be provided in @ref TCP_TICK multiples, i.e., in us. Note that
+ * timestamps are measured as ms ticks so they must be converted before
+ * calling this function.
*/
static void
tcp_estimate_rtt (tcp_connection_t * tc, u32 mrtt)
{
int err, diff;
- if (tc->srtt != 0)
- {
- err = mrtt - tc->srtt;
-
- /* XXX Drop in RTT results in RTTVAR increase and bigger RTO.
- * The increase should be bound */
- tc->srtt = clib_max ((int) tc->srtt + (err >> 3), 1);
- diff = (clib_abs (err) - (int) tc->rttvar) >> 2;
- tc->rttvar = clib_max ((int) tc->rttvar + diff, 1);
- }
- else
- {
- /* First measurement. */
- tc->srtt = mrtt;
- tc->rttvar = mrtt >> 1;
- }
+ err = mrtt - tc->srtt;
+ tc->srtt = clib_max ((int) tc->srtt + (err >> 3), 1);
+ diff = (clib_abs (err) - (int) tc->rttvar) >> 2;
+ tc->rttvar = clib_max ((int) tc->rttvar + diff, 1);
}
static inline void
@@ -506,8 +501,8 @@ tcp_update_rtt (tcp_connection_t * tc, tcp_rate_sample_t * rs, u32 ack)
* seq_lt (tc->snd_una, ack). This is a condition for calling update_rtt */
else if (tcp_opts_tstamp (&tc->rcv_opts) && tc->rcv_opts.tsecr)
{
- u32 now = tcp_tstamp (tc);
- mrtt = clib_max (now - tc->rcv_opts.tsecr, 1);
+ mrtt = clib_max (tcp_tstamp (tc) - tc->rcv_opts.tsecr, 1);
+ mrtt *= TCP_TSTP_TO_HZ;
}
estimate_rtt:
@@ -543,8 +538,8 @@ tcp_estimate_initial_rtt (tcp_connection_t * tc)
}
else
{
- mrtt = tcp_time_now_w_thread (thread_index) - tc->rcv_opts.tsecr;
- mrtt = clib_max (mrtt, 1);
+ mrtt = tcp_tstamp (tc) - tc->rcv_opts.tsecr;
+ mrtt = clib_max (mrtt, 1) * TCP_TSTP_TO_HZ;
/* Due to retransmits we don't know the initial mrtt */
if (tc->rto_boff && mrtt > 1 * THZ)
mrtt = 1 * THZ;
@@ -552,7 +547,11 @@ tcp_estimate_initial_rtt (tcp_connection_t * tc)
}
if (mrtt > 0 && mrtt < TCP_RTT_MAX)
- tcp_estimate_rtt (tc, mrtt);
+ {
+ /* First measurement as per RFC 6298 */
+ tc->srtt = mrtt;
+ tc->rttvar = mrtt >> 1;
+ }
tcp_update_rto (tc);
}