netdev - Re: [PATCH v2] TCP: avoid to send keepalive probes if it is receiving data

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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.