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Message-ID: <alpine.DEB.2.00.1004182328370.19304@melkinpaasi.cs.helsinki.fi>
Date: Sun, 18 Apr 2010 23:34:15 +0300 (EEST)
From: "Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
To: Eric Dumazet <eric.dumazet@...il.com>
cc: Flavio Leitner <fleitner@...hat.com>,
Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH v2] TCP: avoid to send keepalive probes if it is receiving
data
On Sun, 18 Apr 2010, Eric Dumazet wrote:
> Le dimanche 18 avril 2010 à 11:55 -0300, Flavio Leitner a écrit :
> > RFC 1122 says the following:
> > ...
> > Keep-alive packets MUST only be sent when no data or
> > acknowledgement packets have been received for the
> > connection within an interval.
> > ...
> >
> > Fix this by storing the timestamp of last received data
> > packet and checking for it when the keepalive timer expires.
> >
> > -v2 fix do_tcp_setsockopt() as pointed by Eric Dumazet <eric.dumazet@...il.com>
> >
> > Signed-off-by: Flavio Leitner <fleitner@...hat.com>
>
>
> I find this patch very welcome, and we could easily use this new
> lrcvtime information available in diagnostic tools (ss command)
>
> But are you sure you update it for all valid packets ?
>
> If we receive a pure ACK, it seems you do not ...
I fail to see why the addition of this new variable is necessary at all,
could either of you enlight me why exactly it's necessary and rcv_tstamp
will not suffice?
> > ---
> > include/linux/tcp.h | 1 +
> > net/ipv4/tcp.c | 5 ++++-
> > net/ipv4/tcp_input.c | 3 +++
> > net/ipv4/tcp_timer.c | 8 ++++++++
> > 4 files changed, 16 insertions(+), 1 deletions(-)
> >
> > diff --git a/include/linux/tcp.h b/include/linux/tcp.h
> > index a778ee0..405678f 100644
> > --- a/include/linux/tcp.h
> > +++ b/include/linux/tcp.h
> > @@ -314,6 +314,7 @@ struct tcp_sock {
> > u32 snd_sml; /* Last byte of the most recently transmitted small packet */
> > u32 rcv_tstamp; /* timestamp of last received ACK (for keepalives) */
> > u32 lsndtime; /* timestamp of last sent data packet (for restart window) */
> > + u32 lrcvtime; /* timestamp of last received data packet (for keepalives) */
> >
> > /* Data for direct copy to user */
> > struct {
> > diff --git a/net/ipv4/tcp.c b/net/ipv4/tcp.c
> > index 0f8caf6..a4048d7 100644
> > --- a/net/ipv4/tcp.c
> > +++ b/net/ipv4/tcp.c
> > @@ -2298,7 +2298,10 @@ static int do_tcp_setsockopt(struct sock *sk, int level,
> > if (sock_flag(sk, SOCK_KEEPOPEN) &&
> > !((1 << sk->sk_state) &
> > (TCPF_CLOSE | TCPF_LISTEN))) {
> > - __u32 elapsed = tcp_time_stamp - tp->rcv_tstamp;
> > + u32 elapsed = min_t(u32,
> > + tcp_time_stamp - tp->rcv_tstamp,
> > + tcp_time_stamp - tp->lrcvtime);
> > +
> > if (tp->keepalive_time > elapsed)
> > elapsed = tp->keepalive_time - elapsed;
> > else
> > diff --git a/net/ipv4/tcp_input.c b/net/ipv4/tcp_input.c
> > index f240f57..60d2980 100644
> > --- a/net/ipv4/tcp_input.c
> > +++ b/net/ipv4/tcp_input.c
> > @@ -5391,6 +5391,8 @@ no_ack:
> > __kfree_skb(skb);
> > else
> > sk->sk_data_ready(sk, 0);
> > +
> > + tp->lrcvtime = tcp_time_stamp;
> > return 0;
> > }
> > }
> > @@ -5421,6 +5423,7 @@ step5:
> >
> > tcp_data_snd_check(sk);
> > tcp_ack_snd_check(sk);
> > + tp->lrcvtime = tcp_time_stamp;
> > return 0;
> >
> > csum_error:
> > diff --git a/net/ipv4/tcp_timer.c b/net/ipv4/tcp_timer.c
> > index 8a0ab29..74dd804 100644
> > --- a/net/ipv4/tcp_timer.c
> > +++ b/net/ipv4/tcp_timer.c
> > @@ -554,6 +554,14 @@ static void tcp_keepalive_timer (unsigned long data)
> > if (tp->packets_out || tcp_send_head(sk))
> > goto resched;
> >
> > + elapsed = tcp_time_stamp - tp->lrcvtime;
> > +
> > + /* receiving data means alive */
> > + if (elapsed < keepalive_time_when(tp)) {
> > + elapsed = keepalive_time_when(tp) - elapsed;
> > + goto resched;
> > + }
> > +
> > elapsed = tcp_time_stamp - tp->rcv_tstamp;
> >
> > if (elapsed >= keepalive_time_when(tp)) {
--
i.
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