ping was causing 2.3m syscalls/s when messages were lost.
this was due to large lock latency.  i'm thinking about changing
the alarm to just interval+waittime rather than to wait for all
the messages.

Reference: /n/atom/patch/applied/pinglocklat
Date: Fri Feb 21 16:46:35 CET 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/cmd/ip/ping.c	Fri Feb 21 16:43:11 2014
+++ /sys/src/cmd/ip/ping.c	Fri Feb 21 16:43:11 2014
@@ -53,6 +53,7 @@
 int quiet;
 int rcvdmsgs;
 int rint;
+int nsecfd;
 ushort firstseq;
 vlong sum;
 int waittime = 5000;
@@ -147,7 +148,7 @@
 clean(ushort seq, vlong now, void *v)
 {
 	int ttl;
-	Req **l, *r;
+	Req **l, *r, *rlost, **rr;
 
 	ttl = 0;
 	if (v) {
@@ -156,6 +157,8 @@
 		else
 			ttl = ((Ip6hdr *)v)->ttl;
 	}
+	rlost = nil;
+	rr = &rlost;
 	lock(&listlock);
 	last = nil;
 	for(l = &first; *l; ){
@@ -167,20 +170,27 @@
 			reply(r, v);
 		}
 
-		if(now-r->time > MINUTE){
+		if(now-r->time >= MINUTE){
 			*l = r->next;
-			r->rtt = now-r->time;
-			if(v)
-				r->ttl = ttl;
-			if(r->replied == 0)
-				lost(r, v);
-			free(r);
+			r->next = nil;
+			*rr = r;
+			rr = &(*rr)->next;
 		}else{
 			last = r;
 			l = &r->next;
 		}
 	}
 	unlock(&listlock);
+
+	for(; (r = rlost) != nil;){
+		rlost = rlost->next;
+		r->rtt = now-r->time;
+		if(v)
+			r->ttl = ttl;
+		if(r->replied == 0)
+			lost(r, v);
+		free(r);
+	}
 }
 
 static uchar loopbacknet[IPaddrlen] = {
@@ -279,7 +289,8 @@
 		r->seq = seq;
 		r->next = nil;
 		r->replied = 0;
-		r->time = nsec();	/* avoid early free in reply! */
+//		nsecfd = bintime(nsecfd, &r->time, nil, nil);	/* avoid early free in reply! */
+		r->time = 1ull<<62;
 		lock(&listlock);
 		if(first == nil)
 			first = r;
@@ -287,7 +298,7 @@
 			last->next = r;
 		last = r;
 		unlock(&listlock);
-		r->time = nsec();
+		nsecfd = bintime(nsecfd, &r->time, nil, nil);
 		if(write(fd, buf, msglen) < msglen){
 			fprint(2, "%s: write failed: %r\n", argv0);
 			return;
@@ -310,9 +321,10 @@
 	sum = 0;
 	while(lostmsgs+rcvdmsgs < nmsg){
 		alarm((nmsg-lostmsgs-rcvdmsgs)*interval+waittime);
+//		alarm(interval+waittime);
 		n = read(fd, buf, sizeof buf);
 		alarm(0);
-		now = nsec();
+		nsecfd = bintime(nsecfd, &now, nil, nil);
 		if(n <= 0){	/* read interrupted - time to go */
 			clean(0, now+MINUTE, nil);
 			continue;
@@ -490,7 +502,7 @@
 	int fd, msglen, interval, nmsg;
 	char *ds;
 
-	nsec();		/* make sure time file is already open */
+	nsecfd = bintime(-1, nil, nil, nil);
 
 	fmtinstall('V', eipfmt);
 	fmtinstall('I', eipfmt);