tcp sync cache refcount improvement

[Alexander Bluhm]

Hi,

Avoid a useless increment and decrement of of the tcp syn cache
refcount by unexpanding the SYN_CACHE_TIMER_ARM() macro in the timer
callback.

ok?

bluhm

Index: netinet/tcp_input.c
===================================================================
RCS file: /data/mirror/openbsd/cvs/src/sys/netinet/tcp_input.c,v
retrieving revision 1.390
diff -u -p -r1.390 tcp_input.c
--- netinet/tcp_input.c 28 Aug 2023 14:50:01 -0000      1.390
+++ netinet/tcp_input.c 3 Sep 2023 18:04:13 -0000
@@ -3159,19 +3159,6 @@ syn_cache_put(struct syn_cache *sc)
        pool_put(&syn_cache_pool, sc);
 }
 
-/*
- * We don't estimate RTT with SYNs, so each packet starts with the default
- * RTT and each timer step has a fixed timeout value.
- */
-#define        SYN_CACHE_TIMER_ARM(sc)                                         
\
-do {                                                                   \
-       TCPT_RANGESET((sc)->sc_rxtcur,                                  \
-           TCPTV_SRTTDFLT * tcp_backoff[(sc)->sc_rxtshift], TCPTV_MIN, \
-           TCPTV_REXMTMAX);                                            \
-       if (timeout_add_msec(&(sc)->sc_timer, (sc)->sc_rxtcur))         \
-               refcnt_take(&(sc)->sc_refcnt);                          \
-} while (/*CONSTCOND*/0)
-
 void
 syn_cache_init(void)
 {
@@ -3300,11 +3287,17 @@ syn_cache_insert(struct syn_cache *sc, s
        }
 
        /*
-        * Initialize the entry's timer.
+        * Initialize the entry's timer.  We don't estimate RTT
+        * with SYNs, so each packet starts with the default RTT
+        * and each timer step has a fixed timeout value.
         */
        sc->sc_rxttot = 0;
        sc->sc_rxtshift = 0;
-       SYN_CACHE_TIMER_ARM(sc);
+       TCPT_RANGESET(sc->sc_rxtcur,
+           TCPTV_SRTTDFLT * tcp_backoff[sc->sc_rxtshift], TCPTV_MIN,
+           TCPTV_REXMTMAX);
+       if (timeout_add_msec(&sc->sc_timer, sc->sc_rxtcur))
+               refcnt_take(&sc->sc_refcnt);
 
        /* Link it from tcpcb entry */
        refcnt_take(&sc->sc_refcnt);
@@ -3365,15 +3358,12 @@ syn_cache_timer(void *arg)
 
        /* Advance the timer back-off. */
        sc->sc_rxtshift++;
-       SYN_CACHE_TIMER_ARM(sc);
+       TCPT_RANGESET(sc->sc_rxtcur,
+           TCPTV_SRTTDFLT * tcp_backoff[sc->sc_rxtshift], TCPTV_MIN,
+           TCPTV_REXMTMAX);
+       if (!timeout_add_msec(&sc->sc_timer, sc->sc_rxtcur))
+               syn_cache_put(sc);
 
-       /*
-        * Decrement reference of this timer.  We know there is another timer
-        * as we just added it.  So just deref, free is not necessary.
-        */
-       lastref = refcnt_rele(&sc->sc_refcnt);
-       KASSERT(lastref == 0);
-       (void)lastref;
        NET_UNLOCK();
        return;