On Mon, Dec 07, 2015 at 10:00:11AM +0100, Per Hurtig wrote:
> This patch implements the RTO restart modification (RTOR). When data is
> ACKed, and the RTO timer is restarted, the time elapsed since the last
> outstanding segment was transmitted is subtracted from the calculated RTO
> value. This way, the RTO timer will expire after exactly RTO seconds, and
> not RTO + RTT [+ delACK] seconds.
>
> This patch also implements a new sysctl (tcp_timer_restart) that is used
> to control the timer restart behavior.
>
> Signed-off-by: Per Hurtig <per.hur...@kau.se>
> ---
> Documentation/networking/ip-sysctl.txt | 12 ++++++++++++
> include/net/tcp.h | 4 ++++
> net/ipv4/sysctl_net_ipv4.c | 10 ++++++++++
> net/ipv4/tcp_input.c | 24 ++++++++++++++++++++++++
> 4 files changed, 50 insertions(+)
>
> diff --git a/Documentation/networking/ip-sysctl.txt
> b/Documentation/networking/ip-sysctl.txt
> index 2ea4c45..4094128 100644
> --- a/Documentation/networking/ip-sysctl.txt
> +++ b/Documentation/networking/ip-sysctl.txt
(snip)
> @@ -2997,6 +2998,18 @@ static void tcp_cong_avoid(struct sock *sk, u32 ack,
> u32 acked)
> tcp_sk(sk)->snd_cwnd_stamp = tcp_time_stamp;
> }
>
> +static u32 tcp_unsent_pkts(const struct sock *sk)
> +{
> + struct sk_buff *skb = tcp_send_head(sk);
> + u32 pkts = 0;
> +
> + if (skb)
> + tcp_for_write_queue_from(skb, sk)
> + pkts += tcp_skb_pcount(skb);
> +
> + return pkts;
> +}
> +
> /* Restart timer after forward progress on connection.
> * RFC2988 recommends to restart timer to now+rto.
> */
> @@ -3027,6 +3040,17 @@ void tcp_rearm_rto(struct sock *sk)
> */
> if (delta > 0)
> rto = delta;
> + } else if (icsk->icsk_pending == ICSK_TIME_RETRANS &&
> + (sysctl_tcp_timer_restart == 1 ||
> + sysctl_tcp_timer_restart == 3) &&
> + (tp->packets_out + tcp_unsent_pkts(sk) <
> + TCP_RTORESTART_THRESH)) {
(snip)
By when this gets hit, you could have a big write queue.
What about wrapping at least this this condition
tp->packets_out + tcp_unsent_pkts(sk) < TCP_RTORESTART_THRESH
in its own check function? Like:
+static bool tcp_can_rtor(const struct sock *sk)
+{
+ struct sk_buff *skb = tcp_send_head(sk);
+ s32 target = TCP_RTORESTART_THRESH - tp->packets_out;
+
+ if (target <= 0)
+ return false;
+
+ if (skb) {
+ tcp_for_write_queue_from(skb, sk) {
+ target -= tcp_skb_pcount(skb);
+ if (target <= 0)
+ return false;
+ }
+ }
+
+ return true;
+}
This way it will only traverse what is needed for the check itself.
Marcelo
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