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Date: Mon, 12 May 2014 21:41:28 -0700
From: Yuchung Cheng <ycheng@...gle.com>
To: Florian Westphal <fw@...len.de>
Cc: netdev <netdev@...r.kernel.org>,
Daniel Borkmann <dborkman@...hat.com>,
Glenn Judd <glenn.judd@...ganstanley.com>
Subject: Re: [PATCH 4/5] net: tcp: more detailed ACK events, and events for CE
marked packets
On Mon, May 12, 2014 at 1:59 PM, Florian Westphal <fw@...len.de> wrote:
>
> DataCenter TCP (DCTCP) determines cwnd growth based on ECN information
> and ACK properties, e.g. ACK that updates window is treated differently
> than DUPACK.
>
> Also DCTCP needs information whether ACK was delayed ACK. Furthermore,
> DCTCP also implements a CE state machine that keeps track of CE markings
> of incoming packets.
>
> Therefore, extend the congestion control framework to provide these
> event types, so that DCTCP can be properly implemented as a normal
> congestion algorithm module outside the core stack.
>
> Joint work with Daniel Borkmann and Glenn Judd.
>
> Signed-off-by: Daniel Borkmann <dborkman@...hat.com>
> Signed-off-by: Glenn Judd <glenn.judd@...ganstanley.com>
> Signed-off-by: Florian Westphal <fw@...len.de>
> ---
> include/net/tcp.h | 9 ++++++++-
> net/ipv4/tcp_input.c | 22 ++++++++++++++++++----
> net/ipv4/tcp_output.c | 4 ++++
> 3 files changed, 30 insertions(+), 5 deletions(-)
>
> diff --git a/include/net/tcp.h b/include/net/tcp.h
> index 0d767d2..56bf383 100644
> --- a/include/net/tcp.h
> +++ b/include/net/tcp.h
> @@ -754,10 +754,17 @@ enum tcp_ca_event {
> CA_EVENT_CWND_RESTART, /* congestion window restart */
> CA_EVENT_COMPLETE_CWR, /* end of congestion recovery */
> CA_EVENT_LOSS, /* loss timeout */
> + CA_EVENT_ECN_NO_CE, /* ECT set, but not CE marked */
> + CA_EVENT_ECN_IS_CE, /* received CE marked IP packet */
> + CA_EVENT_DELAYED_ACK, /* Delayed ack is sent */
> + CA_EVENT_NON_DELAYED_ACK,
do we need NON_DELAYED_ACK event? is there a third kind?
> };
>
> +/* information about inbound ACK, passed to cong_ops->in_ack_event() */
> enum tcp_ca_ack_event_flags {
> - CA_ACK_SLOWPATH = (1 << 0),
> + CA_ACK_SLOWPATH = (1 << 0), /* in slow path processing */
> + CA_ACK_WIN_UPDATE = (1 << 1), /* ACK updated window */
> + CA_ACK_ECE = (1 << 2), /* ECE bit is set on ack */
> };
>
>
> /*
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index 7fab1da..bf0f734 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -232,14 +232,21 @@ static inline void TCP_ECN_check_ce(struct tcp_sock *tp, const struct sk_buff *s
> tcp_enter_quickack_mode((struct sock *)tp);
> break;
> case INET_ECN_CE:
> + if (tcp_ca_needs_ecn((struct sock *)tp))
> + tcp_ca_event((struct sock *)tp, CA_EVENT_ECN_IS_CE);
> +
> if (!(tp->ecn_flags & TCP_ECN_DEMAND_CWR)) {
> /* Better not delay acks, sender can have a very low cwnd */
> tcp_enter_quickack_mode((struct sock *)tp);
> tp->ecn_flags |= TCP_ECN_DEMAND_CWR;
> }
> - /* fallinto */
> + tp->ecn_flags |= TCP_ECN_SEEN;
> + break;
> default:
> + if (tcp_ca_needs_ecn((struct sock *)tp))
> + tcp_ca_event((struct sock *)tp, CA_EVENT_ECN_NO_CE);
> tp->ecn_flags |= TCP_ECN_SEEN;
> + break;
> }
> }
>
> @@ -3421,10 +3428,12 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
> tp->snd_una = ack;
> flag |= FLAG_WIN_UPDATE;
>
> - tcp_in_ack_event(sk, 0);
> + tcp_in_ack_event(sk, CA_ACK_WIN_UPDATE);
These CA_ACK_xxx are identical to the ACK flag so might as well just
pass the flag to the event handler?
>
> NET_INC_STATS_BH(sock_net(sk), LINUX_MIB_TCPHPACKS);
> } else {
> + u32 ack_ev_flags = CA_ACK_SLOWPATH;
> +
> if (ack_seq != TCP_SKB_CB(skb)->end_seq)
> flag |= FLAG_DATA;
> else
> @@ -3436,10 +3445,15 @@ static int tcp_ack(struct sock *sk, const struct sk_buff *skb, int flag)
> flag |= tcp_sacktag_write_queue(sk, skb, prior_snd_una,
> &sack_rtt_us);
>
> - if (TCP_ECN_rcv_ecn_echo(tp, tcp_hdr(skb)))
> + if (TCP_ECN_rcv_ecn_echo(tp, tcp_hdr(skb))) {
> flag |= FLAG_ECE;
> + ack_ev_flags |= CA_ACK_ECE;
> + }
> +
> + if (flag & FLAG_WIN_UPDATE)
> + ack_ev_flags |= CA_ACK_WIN_UPDATE;
>
> - tcp_in_ack_event(sk, CA_ACK_SLOWPATH);
> + tcp_in_ack_event(sk, ack_ev_flags);
> }
>
> /* We passed data and got it acked, remove any soft error
> diff --git a/net/ipv4/tcp_output.c b/net/ipv4/tcp_output.c
> index 1f983dd..1f5e04a 100644
> --- a/net/ipv4/tcp_output.c
> +++ b/net/ipv4/tcp_output.c
> @@ -3119,6 +3119,8 @@ void tcp_send_delayed_ack(struct sock *sk)
> int ato = icsk->icsk_ack.ato;
> unsigned long timeout;
>
> + tcp_ca_event(sk, CA_EVENT_DELAYED_ACK);
> +
> if (ato > TCP_DELACK_MIN) {
> const struct tcp_sock *tp = tcp_sk(sk);
> int max_ato = HZ / 2;
> @@ -3175,6 +3177,8 @@ void tcp_send_ack(struct sock *sk)
> if (sk->sk_state == TCP_CLOSE)
> return;
>
> + tcp_ca_event(sk, CA_EVENT_NON_DELAYED_ACK);
> +
> /* We are not putting this on the write queue, so
> * tcp_transmit_skb() will set the ownership to this
> * sock.
> --
> 1.8.1.5
>
> --
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