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authorFlorin Coras <fcoras@cisco.com>2020-06-07 20:06:56 +0000
committerFlorin Coras <florin.coras@gmail.com>2020-06-08 18:44:34 +0000
commit8ddd19bf7bbb351a45be1baf6cf670b9fa3360b0 (patch)
tree384a28c9a6301411b2f1218adaeb288e955534e2
parent0a67b48f1d1065d250191657810bd5cd0b718c39 (diff)
tcp: improve rtt estimation with rate sampling
Type: improvement Signed-off-by: Florin Coras <fcoras@cisco.com> Change-Id: I25043da84b2f2b3f37024ecfedac535df3004ea5
-rw-r--r--src/vnet/tcp/tcp_input.c47
1 files changed, 29 insertions, 18 deletions
diff --git a/src/vnet/tcp/tcp_input.c b/src/vnet/tcp/tcp_input.c
index 964afe36751..cc373f5b665 100644
--- a/src/vnet/tcp/tcp_input.c
+++ b/src/vnet/tcp/tcp_input.c
@@ -426,8 +426,6 @@ acceptable:
* Note that although 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.
- *
- * TODO support us rtt resolution
*/
static void
tcp_estimate_rtt (tcp_connection_t * tc, u32 mrtt)
@@ -452,16 +450,28 @@ tcp_estimate_rtt (tcp_connection_t * tc, u32 mrtt)
}
}
+static inline void
+tcp_estimate_rtt_us (tcp_connection_t * tc, f64 mrtt)
+{
+ tc->mrtt_us = tc->mrtt_us + (mrtt - tc->mrtt_us) * 0.125;
+}
+
/**
- * Update RTT estimate and RTO timer
+ * Update rtt estimate
*
- * Measure RTT: We have two sources of RTT measurements: TSOPT and ACK
- * timing. Middle boxes are known to fiddle with TCP options so we
- * should give higher priority to ACK timing.
+ * We have potentially three sources of rtt measurements:
*
- * This should be called only if previously sent bytes have been acked.
+ * TSOPT difference between current and echoed timestamp. It has ms
+ * precision and can be computed per ack
+ * ACK timing one sequence number is tracked per rtt with us (micro second)
+ * precision.
+ * rate sample if enabled, all outstanding bytes are tracked with us
+ * precision. Every ack and sack are a rtt sample
*
- * return 1 if valid rtt 0 otherwise
+ * Middle boxes are known to fiddle with TCP options so we give higher
+ * priority to ACK timing.
+ *
+ * For now, rate sample rtts are only used under congestion.
*/
static int
tcp_update_rtt (tcp_connection_t * tc, tcp_rate_sample_t * rs, u32 ack)
@@ -473,19 +483,19 @@ tcp_update_rtt (tcp_connection_t * tc, tcp_rate_sample_t * rs, u32 ack)
if (tcp_in_cong_recovery (tc))
{
/* Accept rtt estimates for samples that have not been retransmitted */
- if ((tc->cfg_flags & TCP_CFG_F_RATE_SAMPLE)
- && !(rs->flags & TCP_BTS_IS_RXT))
- {
- mrtt = rs->rtt_time * THZ;
- goto estimate_rtt;
- }
- goto done;
+ if (!(tc->cfg_flags & TCP_CFG_F_RATE_SAMPLE)
+ || (rs->flags & TCP_BTS_IS_RXT))
+ goto done;
+ if (rs->rtt_time)
+ tcp_estimate_rtt_us (tc, rs->rtt_time);
+ mrtt = rs->rtt_time * THZ;
+ goto estimate_rtt;
}
if (tc->rtt_ts && seq_geq (ack, tc->rtt_seq))
{
f64 sample = tcp_time_now_us (tc->c_thread_index) - tc->rtt_ts;
- tc->mrtt_us = tc->mrtt_us + (sample - tc->mrtt_us) * 0.125;
+ tcp_estimate_rtt_us (tc, sample);
mrtt = clib_max ((u32) (sample * THZ), 1);
/* Allow measuring of a new RTT */
tc->rtt_ts = 0;
@@ -1048,10 +1058,11 @@ process_ack:
if (tc->cfg_flags & TCP_CFG_F_RATE_SAMPLE)
tcp_bt_sample_delivery_rate (tc, &rs);
- if (tc->bytes_acked)
+ if (tc->bytes_acked + tc->sack_sb.last_sacked_bytes)
{
- tcp_program_dequeue (wrk, tc);
tcp_update_rtt (tc, &rs, vnet_buffer (b)->tcp.ack_number);
+ if (tc->bytes_acked)
+ tcp_program_dequeue (wrk, tc);
}
TCP_EVT (TCP_EVT_ACK_RCVD, tc);