netdev - Re: [RFC PATCH v6 net-next 3/4] tcp: add in_flight to tcp_skb

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Date:	Thu, 27 Aug 2015 15:00:43 -0700
From:	Yuchung Cheng <ycheng@...gle.com>
To:	Lawrence Brakmo <brakmo@...com>
Cc:	netdev <netdev@...r.kernel.org>, Kernel Team <kernel-team@...com>,
	Neal Cardwell <ncardwell@...gle.com>,
	Eric Dumazet <eric.dumazet@...il.com>,
	Stephen Hemminger <stephen@...workplumber.org>,
	Kenneth Klette Jonassen <kennetkl@....uio.no>
Subject: Re: [RFC PATCH v6 net-next 3/4] tcp: add in_flight to tcp_skb_cb

On Tue, Aug 25, 2015 at 4:33 PM, Lawrence Brakmo <brakmo@...com> wrote:
> Add in_flight (bytes in flight when packet was sent) field
> to tx component of tcp_skb_cb and make it available to
> congestion modules' pkts_acked() function through the
> ack_sample function argument.
>
> Signed-off-by: Lawrence Brakmo <brakmo@...com>
> ---
>  include/net/tcp.h     | 2 ++
>  net/ipv4/tcp_input.c  | 5 ++++-
>  net/ipv4/tcp_output.c | 4 +++-
>  3 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index a086a98..cdd93e5 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -757,6 +757,7 @@ struct tcp_skb_cb {
>         union {
>                 struct {
>                         /* There is space for up to 20 bytes */
> +                       __u32 in_flight;/* Bytes in flight when packet sent */
>                 } tx;   /* only used for outgoing skbs */
>                 union {
>                         struct inet_skb_parm    h4;
> @@ -842,6 +843,7 @@ union tcp_cc_info;
>  struct ack_sample {
>         u32 pkts_acked;
>         s32 rtt_us;
> +       u32 in_flight;
>  };
>
>  struct tcp_congestion_ops {
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index f506a0a..338e6bb 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -3069,6 +3069,7 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
>         long ca_rtt_us = -1L;
>         struct sk_buff *skb;
>         u32 pkts_acked = 0;
> +       u32 last_in_flight = 0;
>         bool rtt_update;
>         int flag = 0;
>
> @@ -3108,6 +3109,7 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
>                         if (!first_ackt.v64)
>                                 first_ackt = last_ackt;
>
> +                       last_in_flight = TCP_SKB_CB(skb)->tx.in_flight;
>                         reord = min(pkts_acked, reord);
>                         if (!after(scb->end_seq, tp->high_seq))
>                                 flag |= FLAG_ORIG_SACK_ACKED;
> @@ -3197,7 +3199,8 @@ static int tcp_clean_rtx_queue(struct sock *sk, int prior_fackets,
>         }
>
>         if (icsk->icsk_ca_ops->pkts_acked) {
> -               struct ack_sample sample = {pkts_acked, ca_rtt_us};
> +               struct ack_sample sample = {pkts_acked, ca_rtt_us,
> +                                           last_in_flight};
>
>                 icsk->icsk_ca_ops->pkts_acked(sk, &sample);
>         }
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index 444ab5b..244d201 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -920,9 +920,12 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
>         int err;
>
>         BUG_ON(!skb || !tcp_skb_pcount(skb));
> +       tp = tcp_sk(sk);
>
>         if (clone_it) {
>                 skb_mstamp_get(&skb->skb_mstamp);
> +               TCP_SKB_CB(skb)->tx.in_flight = TCP_SKB_CB(skb)->end_seq
> +                       - tp->snd_una;
what if skb is a retransmitted packet? e.g. the first retransmission
in fast recovery would always record an inflight of 1 packet?

>
>                 if (unlikely(skb_cloned(skb)))
>                         skb = pskb_copy(skb, gfp_mask);
> @@ -933,7 +936,6 @@ static int tcp_transmit_skb(struct sock *sk, struct sk_buff *skb, int clone_it,
>         }
>
>         inet = inet_sk(sk);
> -       tp = tcp_sk(sk);
>         tcb = TCP_SKB_CB(skb);
>         memset(&opts, 0, sizeof(opts));
>
> --
> 1.8.1
>
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