netdev - Re: [PATCH] tcp: provide tx timestamps for partial writes

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Message-ID: <CACSApvYE-DQ_B0=82+V0XtNV926mobAUJ5rNEg4nv7q9CPDTWA@mail.gmail.com>
Date:   Wed, 4 Jan 2017 10:04:50 -0500
From:   Soheil Hassas Yeganeh <soheil@...gle.com>
To:     Eric Dumazet <eric.dumazet@...il.com>
Cc:     David Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Willem de Bruijn <willemb@...gle.com>,
        Yuchung Cheng <ycheng@...gle.com>,
        Eric Dumazet <edumazet@...gle.com>,
        Neal Cardwell <ncardwell@...gle.com>,
        Martin KaFai Lau <kafai@...com>
Subject: Re: [PATCH] tcp: provide tx timestamps for partial writes

On Wed, Jan 4, 2017 at 7:55 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
>
> On Tue, 2017-01-03 at 10:22 -0500, Soheil Hassas Yeganeh wrote:
> > On Mon, Jan 2, 2017 at 3:23 PM, Soheil Hassas Yeganeh <soheil@...gle.com> wrote:
> > > On Mon, Jan 2, 2017 at 3:20 PM, Soheil Hassas Yeganeh
> > > <soheil.kdev@...il.com> wrote:
> > >> From: Soheil Hassas Yeganeh <soheil@...gle.com>
> > >>
> > >> For TCP sockets, tx timestamps are only captured when the user data
> > >> is successfully and fully written to the socket. In many cases,
> > >> however, TCP writes can be partial for which no timestamp is
> > >> collected.
> > >>
> > >> Collect timestamps when the user data is partially copied into
> > >> the socket.
> > >>
> > >> Signed-off-by: Soheil Hassas Yeganeh <soheil@...gle.com>
> > >> Cc: Willem de Bruijn <willemb@...gle.com>
> > >> Cc: Yuchung Cheng <ycheng@...gle.com>
> > >> Cc: Eric Dumazet <edumazet@...gle.com>
> > >> Cc: Neal Cardwell <ncardwell@...gle.com>
> > >> Cc: Martin KaFai Lau <kafai@...com>
> > >> ---
> > >>  net/ipv4/tcp.c | 8 ++++++--
> > >>  1 file changed, 6 insertions(+), 2 deletions(-)
> > >>
> > >> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> > >> index 2e3807d..c207b16 100644
> > >> --- a/net/ipv4/tcp.c
> > >> +++ b/net/ipv4/tcp.c
> > >> @@ -992,8 +992,10 @@ static ssize_t do_tcp_sendpages(struct sock *sk, struct page *page, int offset,
> > >>         return copied;
> > >>
> > >>  do_error:
> > >> -       if (copied)
> > >> +       if (copied) {
> > >> +               tcp_tx_timestamp(sk, sk->sk_tsflags, tcp_write_queue_tail(sk));
> > >>                 goto out;
> > >> +       }
> > >>  out_err:
> > >>         /* make sure we wake any epoll edge trigger waiter */
> > >>         if (unlikely(skb_queue_len(&sk->sk_write_queue) == 0 &&
> > >> @@ -1329,8 +1331,10 @@ int tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
> > >>         }
> > >>
> > >>  do_error:
> > >> -       if (copied + copied_syn)
> > >> +       if (copied + copied_syn) {
> > >> +               tcp_tx_timestamp(sk, sk->sk_tsflags, tcp_write_queue_tail(sk));
> >
> > Thanks to Willem for noting that this should be sockc.tsflags and not
> > sk->sk_tsflags. I'll send V2 to fix.
>
> Also, why not factorizing a bit and have a single point calling
> tcp_tx_timestamp() ?
>
> This would ease code review quite a bit.

Thanks Eric! will do in V2.

> diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> index 4a044964da6670829e5c47fef52d2cd76360b59f..11357f3bd1f82fa29129dd3ecf4d270feb4a6b1d 100644
> --- a/net/ipv4/tcp.c
> +++ b/net/ipv4/tcp.c
> @@ -958,10 +958,8 @@ static ssize_t do_tcp_sendpages(struct sock *sk, struct page *page, int offset,
>                 copied += copy;
>                 offset += copy;
>                 size -= copy;
> -               if (!size) {
> -                       tcp_tx_timestamp(sk, sk->sk_tsflags, skb);
> +               if (!size)
>                         goto out;
> -               }
>
>                 if (skb->len < size_goal || (flags & MSG_OOB))
>                         continue;
> @@ -987,8 +985,11 @@ static ssize_t do_tcp_sendpages(struct sock *sk, struct page *page, int offset,
>         }
>
>  out:
> -       if (copied && !(flags & MSG_SENDPAGE_NOTLAST))
> -               tcp_push(sk, flags, mss_now, tp->nonagle, size_goal);
> +       if (copied) {
> +               tcp_tx_timestamp(sk, sk->sk_tsflags, tcp_write_queue_tail(sk));
> +               if (!(flags & MSG_SENDPAGE_NOTLAST))
> +                       tcp_push(sk, flags, mss_now, tp->nonagle, size_goal);
> +       }
>         return copied;
>
>  do_error:
> @@ -1281,7 +1282,6 @@ int tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
>
>                 copied += copy;
>                 if (!msg_data_left(msg)) {
> -                       tcp_tx_timestamp(sk, sockc.tsflags, skb);
>                         if (unlikely(flags & MSG_EOR))
>                                 TCP_SKB_CB(skb)->eor = 1;
>                         goto out;
> @@ -1312,8 +1312,10 @@ int tcp_sendmsg(struct sock *sk, struct msghdr *msg, size_t size)
>         }
>
>  out:
> -       if (copied)
> +       if (copied) {
> +               tcp_tx_timestamp(sk, sockc.tsflags, tcp_write_queue_tail(sk));
>                 tcp_push(sk, flags, mss_now, tp->nonagle, size_goal);
> +       }
>  out_nopush:
>         release_sock(sk);
>         return copied + copied_syn;
>
>
>