netdev - Re: [PATCH] tcp: del skb from tsorted_sent

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Message-ID: <CAK6E8=dJzNC7GFTikanKM48Uo5DFZBZGSUVoMy1dCfV0ttNe+g@mail.gmail.com>
Date:   Mon, 29 Aug 2022 17:23:58 -0700
From:   Yuchung Cheng <ycheng@...gle.com>
To:     Yonglong Li <liyonglong@...natelecom.cn>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, dsahern@...nel.org,
        edumazet@...gle.com, kuba@...nel.org, pabeni@...hat.com,
        Neal Cardwell <ncardwell@...gle.com>
Subject: Re: [PATCH] tcp: del skb from tsorted_sent_queue after mark it as lost

On Mon, Aug 29, 2022 at 1:21 AM Yonglong Li <liyonglong@...natelecom.cn> wrote:
>
> if rack is enabled, when skb marked as lost we can remove it from
> tsorted_sent_queue. It will reduces the iterations on tsorted_sent_queue
> in tcp_rack_detect_loss

Did you test the case where an skb is marked lost again after
retransmission? I can't quite remember the reason I avoided this
optimization. let me run some test and get back to you.


>
> Signed-off-by: Yonglong Li <liyonglong@...natelecom.cn>
> ---
>  net/ipv4/tcp_input.c    | 15 +++++++++------
>  net/ipv4/tcp_recovery.c |  1 -
>  2 files changed, 9 insertions(+), 7 deletions(-)
>
> diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> index ab5f0ea..01bd644 100644
> --- a/net/ipv4/tcp_input.c
> +++ b/net/ipv4/tcp_input.c
> @@ -1082,6 +1082,12 @@ static void tcp_notify_skb_loss_event(struct tcp_sock *tp, const struct sk_buff
>         tp->lost += tcp_skb_pcount(skb);
>  }
>
> +static bool tcp_is_rack(const struct sock *sk)
> +{
> +       return READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_recovery) &
> +               TCP_RACK_LOSS_DETECTION;
> +}
> +
>  void tcp_mark_skb_lost(struct sock *sk, struct sk_buff *skb)
>  {
>         __u8 sacked = TCP_SKB_CB(skb)->sacked;
> @@ -1105,6 +1111,9 @@ void tcp_mark_skb_lost(struct sock *sk, struct sk_buff *skb)
>                 TCP_SKB_CB(skb)->sacked |= TCPCB_LOST;
>                 tcp_notify_skb_loss_event(tp, skb);
>         }
> +
> +       if (tcp_is_rack(sk))
> +               list_del_init(&skb->tcp_tsorted_anchor);
>  }
>
>  /* Updates the delivered and delivered_ce counts */
> @@ -2093,12 +2102,6 @@ static inline void tcp_init_undo(struct tcp_sock *tp)
>         tp->undo_retrans = tp->retrans_out ? : -1;
>  }
>
> -static bool tcp_is_rack(const struct sock *sk)
> -{
> -       return READ_ONCE(sock_net(sk)->ipv4.sysctl_tcp_recovery) &
> -               TCP_RACK_LOSS_DETECTION;
> -}
> -
>  /* If we detect SACK reneging, forget all SACK information
>   * and reset tags completely, otherwise preserve SACKs. If receiver
>   * dropped its ofo queue, we will know this due to reneging detection.
> diff --git a/net/ipv4/tcp_recovery.c b/net/ipv4/tcp_recovery.c
> index 50abaa9..ba52ec9e 100644
> --- a/net/ipv4/tcp_recovery.c
> +++ b/net/ipv4/tcp_recovery.c
> @@ -84,7 +84,6 @@ static void tcp_rack_detect_loss(struct sock *sk, u32 *reo_timeout)
>                 remaining = tcp_rack_skb_timeout(tp, skb, reo_wnd);
>                 if (remaining <= 0) {
>                         tcp_mark_skb_lost(sk, skb);
> -                       list_del_init(&skb->tcp_tsorted_anchor);
>                 } else {
>                         /* Record maximum wait time */
>                         *reo_timeout = max_t(u32, *reo_timeout, remaining);
> --
> 1.8.3.1
>