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    Subject[patch 57/67] TCP: Fix and simplify microsecond rtt sampling

    -stable review patch. If anyone has any objections, please let us know.

    ------------------
    From: David Miller <davem@davemloft.net>

    This changes the microsecond RTT sampling so that samples are taken in
    the same way that RTT samples are taken for the RTO calculator: on the
    last segment acknowledged, and only when the segment hasn't been
    retransmitted.

    Signed-off-by: John Heffner <jheffner@psc.edu>
    Acked-by: Stephen Hemminger <shemminger@osdl.org>
    Signed-off-by: David S. Miller <davem@davemloft.net>
    Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

    ---
    net/ipv4/tcp_input.c | 16 ++++++++--------
    1 file changed, 8 insertions(+), 8 deletions(-)

    --- linux-2.6.18.orig/net/ipv4/tcp_input.c
    +++ linux-2.6.18/net/ipv4/tcp_input.c
    @@ -2237,13 +2237,12 @@ static int tcp_tso_acked(struct sock *sk
    return acked;
    }

    -static u32 tcp_usrtt(const struct sk_buff *skb)
    +static u32 tcp_usrtt(struct timeval *tv)
    {
    - struct timeval tv, now;
    + struct timeval now;

    do_gettimeofday(&now);
    - skb_get_timestamp(skb, &tv);
    - return (now.tv_sec - tv.tv_sec) * 1000000 + (now.tv_usec - tv.tv_usec);
    + return (now.tv_sec - tv->tv_sec) * 1000000 + (now.tv_usec - tv->tv_usec);
    }

    /* Remove acknowledged frames from the retransmission queue. */
    @@ -2258,6 +2257,7 @@ static int tcp_clean_rtx_queue(struct so
    u32 pkts_acked = 0;
    void (*rtt_sample)(struct sock *sk, u32 usrtt)
    = icsk->icsk_ca_ops->rtt_sample;
    + struct timeval tv;

    while ((skb = skb_peek(&sk->sk_write_queue)) &&
    skb != sk->sk_send_head) {
    @@ -2306,8 +2306,7 @@ static int tcp_clean_rtx_queue(struct so
    seq_rtt = -1;
    } else if (seq_rtt < 0) {
    seq_rtt = now - scb->when;
    - if (rtt_sample)
    - (*rtt_sample)(sk, tcp_usrtt(skb));
    + skb_get_timestamp(skb, &tv);
    }
    if (sacked & TCPCB_SACKED_ACKED)
    tp->sacked_out -= tcp_skb_pcount(skb);
    @@ -2320,8 +2319,7 @@ static int tcp_clean_rtx_queue(struct so
    }
    } else if (seq_rtt < 0) {
    seq_rtt = now - scb->when;
    - if (rtt_sample)
    - (*rtt_sample)(sk, tcp_usrtt(skb));
    + skb_get_timestamp(skb, &tv);
    }
    tcp_dec_pcount_approx(&tp->fackets_out, skb);
    tcp_packets_out_dec(tp, skb);
    @@ -2333,6 +2331,8 @@ static int tcp_clean_rtx_queue(struct so
    if (acked&FLAG_ACKED) {
    tcp_ack_update_rtt(sk, acked, seq_rtt);
    tcp_ack_packets_out(sk, tp);
    + if (rtt_sample && !(acked & FLAG_RETRANS_DATA_ACKED))
    + (*rtt_sample)(sk, tcp_usrtt(&tv));

    if (icsk->icsk_ca_ops->pkts_acked)
    icsk->icsk_ca_ops->pkts_acked(sk, pkts_acked);
    --
    -
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