commit 88c06f6d501fa66b482952bf1a5375c4f11697f0
Author: Gleb Smirnoff <glebius@FreeBSD.org>
Date:   Tue Jul 14 17:32:54 2026 -0700

    inpcb: net.inet.ip.lport_dest_histgram

diff --git a/sys/netinet/in_pcb.c b/sys/netinet/in_pcb.c
index 45cf963f9460..d86275597f9c 100644
--- a/sys/netinet/in_pcb.c
+++ b/sys/netinet/in_pcb.c
@@ -226,12 +226,19 @@ SYSCTL_COUNTER_U64(_net_inet_ip_rl, OID_AUTO, chgrl, CTLFLAG_RD,
 
 #endif /* INET */
 
+VNET_DEFINE_STATIC(counter_u64_t, lport_dest_histgram[16]);
+#define	V_lport_dest_histgram	VNET(lport_dest_histgram)
+SYSCTL_COUNTER_U64_ARRAY(_net_inet_ip, OID_AUTO, lport_dest_histgram,
+    CTLFLAG_RW | CTLFLAG_VNET, &VNET_NAME(lport_dest_histgram)[0], 16, "");
+
 VNET_DEFINE(uint32_t, in_pcbhashseed);
 static void
 in_pcbhashseed_init(void)
 {
 
 	V_in_pcbhashseed = arc4random();
+
+	COUNTER_ARRAY_ALLOC(V_lport_dest_histgram, 16, M_WAITOK);
 }
 VNET_SYSINIT(in_pcbhashseed_init, SI_SUB_PROTO_DOMAIN, SI_ORDER_FIRST,
     in_pcbhashseed_init, NULL);
@@ -741,6 +748,7 @@ in_pcb_lport_dest(struct inpcbinfo_ctx *ipictx, struct inpcb *inp,
     struct ucred *cred, int lookupflags, u_short *lportp)
 {
 	u_int count, first, last, port, *lastport;
+	u_int cycles;
 	int error;
 	u_short lport;
 #ifdef INET
@@ -811,12 +819,13 @@ in_pcb_lport_dest(struct inpcbinfo_ctx *ipictx, struct inpcb *inp,
 		}
 	}
 
-	for (count = last - first; count > 0; count--) {
+	for (count = last - first, cycles = 0; count > 0; count--) {
 		struct inpcbinfo_ctx tmpctx = {
 			.pcbinfo = ipictx->pcbinfo
 		};
 		struct inpcb *tmpinp = NULL;
 
+		cycles++;
 		lport = htons(port);
 
 		if (fsa != NULL) {
@@ -876,6 +885,8 @@ in_pcb_lport_dest(struct inpcbinfo_ctx *ipictx, struct inpcb *inp,
 
 	*lportp = lport;
 
+	counter_u64_add(V_lport_dest_histgram[31 - __builtin_clz(cycles)], 1);
+
 	return (0);
 }