svn commit: r257367 - stable/10/sys/netinet

[Julian Elischer]

I think 9 needs this too...

On 10/30/13, 5:00 AM, Andre Oppermann wrote:
> Author: andre
> Date: Tue Oct 29 21:00:54 2013
> New Revision: 257367
> URL: http://svnweb.freebsd.org/changeset/base/257367
>
> Log:
>    MFC r256920:
>    
>      The TCP delayed ACK logic isn't aware of LRO passing up large aggregated
>      segments thinking it received only one segment. This causes it to enable
>      the delay the ACK for 100ms to wait for another segment which may never
>      come because all the data was received already.
>    
>      Doing delayed ACK for LRO segments is bogus for two reasons: a) it pushes
>      us further away from acking every other packet; b) it introduces additional
>      delay in responding to the sender.  The latter is especially bad because it
>      is in the nature of LRO to aggregated all segments of a burst with no more
>      coming until an ACK is sent back.
>    
>      Change the delayed ACK logic to detect LRO segments by being larger than
>      the MSS for this connection and issuing an immediate ACK for them to keep
>      the ACK clock ticking without interruption.
>    
>      Reported by:  julian, cperciva
>      Tested by:    cperciva
>      Reviewed by:  lstewart
>    
>    Approved by:    re (glebius)
>
> Modified:
>    stable/10/sys/netinet/tcp_input.c
> Directory Properties:
>    stable/10/sys/   (props changed)
>
> Modified: stable/10/sys/netinet/tcp_input.c
> ==============================================================================
> --- stable/10/sys/netinet/tcp_input.c	Tue Oct 29 20:53:09 2013	(r257366)
> +++ stable/10/sys/netinet/tcp_input.c	Tue Oct 29 21:00:54 2013	(r257367)
> @@ -508,10 +508,13 @@ do { \
>    *	  the ack that opens up a 0-sized window and
>    *		- delayed acks are enabled or
>    *		- this is a half-synchronized T/TCP connection.
> + *	- the segment size is not larger than the MSS and LRO wasn't used
> + *	  for this segment.
>    */
> -#define DELAY_ACK(tp)							\
> +#define DELAY_ACK(tp, tlen)						\
>   	((!tcp_timer_active(tp, TT_DELACK) &&				\
>   	    (tp->t_flags & TF_RXWIN0SENT) == 0) &&			\
> +	    (tlen <= tp->t_maxopd) &&					\
>   	    (V_tcp_delack_enabled || (tp->t_flags & TF_NEEDSYN)))
>   
>   /*
> @@ -1863,7 +1866,7 @@ tcp_do_segment(struct mbuf *m, struct tc
>   			}
>   			/* NB: sorwakeup_locked() does an implicit unlock. */
>   			sorwakeup_locked(so);
> -			if (DELAY_ACK(tp)) {
> +			if (DELAY_ACK(tp, tlen)) {
>   				tp->t_flags |= TF_DELACK;
>   			} else {
>   				tp->t_flags |= TF_ACKNOW;
> @@ -1954,7 +1957,7 @@ tcp_do_segment(struct mbuf *m, struct tc
>   			 * If there's data, delay ACK; if there's also a FIN
>   			 * ACKNOW will be turned on later.
>   			 */
> -			if (DELAY_ACK(tp) && tlen != 0)
> +			if (DELAY_ACK(tp, tlen) && tlen != 0)
>   				tcp_timer_activate(tp, TT_DELACK,
>   				    tcp_delacktime);
>   			else
> @@ -2926,7 +2929,7 @@ dodata:							/* XXX */
>   		if (th->th_seq == tp->rcv_nxt &&
>   		    LIST_EMPTY(&tp->t_segq) &&
>   		    TCPS_HAVEESTABLISHED(tp->t_state)) {
> -			if (DELAY_ACK(tp))
> +			if (DELAY_ACK(tp, tlen))
>   				tp->t_flags |= TF_DELACK;
>   			else
>   				tp->t_flags |= TF_ACKNOW;
>