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The code currently resets the keepalive timer each time a packet is

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received on a TCP session that has entered the ESTABLISHED state. This
results in a lot of calls to reset the keepalive timer.

This patch changes the behavior so we set the keepalive timer for the
keepalive idle time (TP_KEEPIDLE). When the keepalive timer fires, it will
first check to see if the session has been idle for TP_KEEPIDLE ticks. If
not, it will reschedule the keepalive timer for the time the session will
have been idle for TP_KEEPIDLE ticks.

For a session with regular communication, the keepalive timer should fire
approximately once every TP_KEEPIDLE ticks. For sessions with irregular
communication, the keepalive timer might fire more often. But, the
disruption from a periodic keepalive timer should be less than the regular
cost of resetting the keepalive timer on every packet.

(FWIW, this change saved approximately 1.73% of the busy CPU cycles on a
particular test system with a heavy TCP output load. Of course, the
actual impact is very specific to the particular hardware and workload.)

Reviewed by:	gallatin, rrs
MFC after:	2 weeks
Sponsored by:	Netflix
Differential Revision:	https://reviews.freebsd.org/D8243
This commit is contained in:
Jonathan T. Looney 2016-10-14 14:57:43 +00:00
parent 1899e205d1
commit 6d172f58a2
3 changed files with 20 additions and 6 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
sys/netinet/tcp_input.c
View File

@ -1565,8 +1565,6 @@ tcp_do_segment(struct mbuf *m, struct tcphdr *th, struct socket *so,
* validation to ignore broken/spoofed segs.
*/
tp->t_rcvtime = ticks;
if (TCPS_HAVEESTABLISHED(tp->t_state))
tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
/*
* Scale up the window into a 32-bit value.

4
sys/netinet/tcp_stacks/fastpath.c
View File

@ -1819,8 +1819,6 @@ tcp_do_segment_fastslow(struct mbuf *m, struct tcphdr *th, struct socket *so,
* validation to ignore broken/spoofed segs.
*/
tp->t_rcvtime = ticks;
if (TCPS_HAVEESTABLISHED(tp->t_state))
tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
/*
* Unscale the window into a 32-bit value.
@ -2266,8 +2264,6 @@ tcp_do_segment_fastack(struct mbuf *m, struct tcphdr *th, struct socket *so,
* validation to ignore broken/spoofed segs.
*/
tp->t_rcvtime = ticks;
if (TCPS_HAVEESTABLISHED(tp->t_state))
tcp_timer_activate(tp, TT_KEEP, TP_KEEPIDLE(tp));
/*
* Unscale the window into a 32-bit value.

20
sys/netinet/tcp_timer.c
View File

@ -468,6 +468,26 @@ tcp_timer_keep(void *xtp)
}
KASSERT((tp->t_timers->tt_flags & TT_STOPPED) == 0,
("%s: tp %p tcpcb can't be stopped here", __func__, tp));
/*
* Because we don't regularly reset the keepalive callout in
* the ESTABLISHED state, it may be that we don't actually need
* to send a keepalive yet. If that occurs, schedule another
* call for the next time the keepalive timer might expire.
*/
if (TCPS_HAVEESTABLISHED(tp->t_state)) {
u_int idletime;
idletime = ticks - tp->t_rcvtime;
if (idletime < TP_KEEPIDLE(tp)) {
callout_reset(&tp->t_timers->tt_keep,
TP_KEEPIDLE(tp) - idletime, tcp_timer_keep, tp);
INP_WUNLOCK(inp);
CURVNET_RESTORE();
return;
}
}
/*
* Keep-alive timer went off; send something
* or drop connection if idle for too long.