netdev - Re: [PATCH net-next] tcp: use SACK RTTs for CC

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Date:	Fri, 30 Jan 2015 09:21:45 -0800
From:	Yuchung Cheng <ycheng@...gle.com>
To:	Kenneth Klette Jonassen <kennetkl@....uio.no>
Cc:	netdev <netdev@...r.kernel.org>,
	Neal Cardwell <ncardwell@...gle.com>
Subject: Re: [PATCH net-next] tcp: use SACK RTTs for CC

On Thu, Jan 29, 2015 at 11:08 AM, Kenneth Klette Jonassen
<kennetkl@....uio.no> wrote:
> Current behavior only passes RTTs from sequentially acked data to CC.
>
> If sender gets a combined ACK for segment 1 and SACK for segment 3, then the
> computed RTT for CC is the time between sending segment 1 and receiving SACK
> for segment 3.
since segment 3 is sent after segment 1, sack_rtt_us <= ca_seq_rtt so
taking a min is not necessary?

>
> Pass the minimum computed RTT from any acked data to CC, i.e. time between
> sending segment 3 and receiving SACK for segment 3.
>
> Signed-off-by: Kenneth Klette Jonassen <kennetkl@....uio.no>
> ---
>  net/ipv4/tcp_input.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index 71fb37c..ed11931 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -3183,8 +3183,10 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
>
>                 tp->fackets_out -= min(pkts_acked, tp->fackets_out);
>
> -               if (ca_ops->pkts_acked)
> -                       ca_ops->pkts_acked(sk, pkts_acked, ca_seq_rtt_us);
> +               if (ca_ops->pkts_acked) {
> +                       long rtt_us = min_t(ulong, ca_seq_rtt_us, sack_rtt_us);
> +                       ca_ops->pkts_acked(sk, pkts_acked, rtt_us);
> +               }
>
>         } else if (skb && rtt_update && sack_rtt_us >= 0 &&
>                    sack_rtt_us > skb_mstamp_us_delta(&now, &skb->skb_mstamp)) {
> --
> 1.9.1
>
> --
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