[TCP]: congestion control API pass RTT in microseconds

This patch changes the API for the callback that is done after an ACK is
received. It solves a couple of issues:

  * Some congestion controls want higher resolution value of RTT
    (controlled by TCP_CONG_RTT_SAMPLE flag). These don't really want a ktime, but
    all compute a RTT in microseconds.

  * Other congestion control could use RTT at jiffies resolution.

To keep API consistent the units should be the same for both cases, just the
resolution should change.

Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 16 insertions, 5 deletions

diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
index fec8a7a4dbaf..4b255fe999d9 100644
--- a/net/ipv4/tcp_input.c
+++ b/net/ipv4/tcp_input.c
@@ -2490,12 +2490,23 @@ static int tcp_clean_rtx_queue(struct sock *sk, __s32 *seq_rtt_p)
                 tcp_ack_update_rtt(sk, acked, seq_rtt);
                 tcp_ack_packets_out(sk);
 
-                /* Is the ACK triggering packet unambiguous? */
-                if (acked & FLAG_RETRANS_DATA_ACKED)
-                        last_ackt = net_invalid_timestamp();
+                if (ca_ops->pkts_acked) {
+                        s32 rtt_us = -1;
+
+                        /* Is the ACK triggering packet unambiguous? */
+                        if (!(acked & FLAG_RETRANS_DATA_ACKED)) {
+                                /* High resolution needed and available? */
+                                if (ca_ops->flags & TCP_CONG_RTT_STAMP &&
+                                    !ktime_equal(last_ackt,
+                                                 net_invalid_timestamp()))
+                                        rtt_us = ktime_us_delta(ktime_get_real(),
+                                                                last_ackt);
+                                else if (seq_rtt > 0)
+                                        rtt_us = jiffies_to_usecs(seq_rtt);
+                        }
 
-                if (ca_ops->pkts_acked)
-                        ca_ops->pkts_acked(sk, pkts_acked, last_ackt);
+                        ca_ops->pkts_acked(sk, pkts_acked, rtt_us);
+                }
         }
 
 #if FASTRETRANS_DEBUG > 0