Index: etc/defaults/rc.conf
===================================================================
--- etc/defaults/rc.conf
+++ etc/defaults/rc.conf
@@ -682,6 +682,9 @@
 
 iovctl_files=""		# Config files for iovctl(8)
 
+irqrebalance_enable="NO"	# Balance IRQs dynamically
+irqrebalance_period=""		# Rebalance period (seconds) (defaults to 60)
+
 ##############################################################
 ### Jail Configuration (see rc.conf(5) manual page) ##########
 ##############################################################
Index: etc/rc.d/irqrebalance
===================================================================
--- /dev/null
+++ etc/rc.d/irqrebalance
@@ -0,0 +1,31 @@
+#!/bin/sh
+#
+# $FreeBSD$
+#
+
+# PROVIDE: irqrebalance
+
+. /etc/rc.subr
+
+name="irqrebalance"
+desc="Dynamically rebalance interrupts across cores depending on load"
+rcvar="irqrebalance_enable"
+command="/libexec/${name}"
+start_precmd="irqrebalance_precmd"
+command_args="&"
+
+irqrebalance_precmd()
+{
+
+	case "${irqrebalance_period}" in
+	'')
+		rc_flags="-f 60"
+		;;
+	*)
+		rc_flags="-f ${irqrebalance_period}"
+		;;
+	esac
+}
+
+load_rc_config $name
+run_rc_command "$1"
Index: libexec/Makefile
===================================================================
--- libexec/Makefile
+++ libexec/Makefile
@@ -9,6 +9,7 @@
 	${_comsat} \
 	${_dma} \
 	getty \
+	${_irqrebalance} \
 	${_mail.local} \
 	${_makewhatis.local} \
 	${_mknetid} \
@@ -58,6 +59,10 @@
 _dma=		dma
 .endif
 
+.if ${MK_IRQREBALANCE} != "no"
+_irqrebalance=	irqrebalance
+.endif
+
 .if ${MK_NIS} != "no"
 _mknetid=	mknetid
 _ypxfr=		ypxfr
Index: libexec/irqrebalance/Makefile
===================================================================
--- /dev/null
+++ libexec/irqrebalance/Makefile
@@ -0,0 +1,9 @@
+# $FreeBSD$
+
+.include <src.opts.mk>
+
+PROG=	irqrebalance
+MAN=
+SRCS=	irqrebalance.c
+
+.include <bsd.prog.mk>
Index: libexec/irqrebalance/irqrebalance.c
===================================================================
--- /dev/null
+++ libexec/irqrebalance/irqrebalance.c
@@ -0,0 +1,222 @@
+/*
+ * Copyright (c) 2017 Dell EMC Isilon
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in
+ *    the documentation and/or other materials provided with the
+ *    distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ *
+ * $FreeBSD $
+ */
+
+#include <sys/param.h>
+#include <sys/cpuset.h>
+#include <sys/sysctl.h>
+
+#include <err.h>
+#include <errno.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+
+struct intr_src {
+	const char *is_name;
+	unsigned long is_count;
+	int is_irq;
+};
+
+static cpuset_t cpus;
+static struct intr_src *intr_sources;
+static char *intrnames;
+
+static void enumerate_irqs(void);
+static void irqshuffle(void);
+
+/*
+ * irqrebalance options:
+ *   -f period
+ *      Rebalance every N seconds.
+ */
+int
+main(int argc, char **argv)
+{
+	int c;
+	time_t period;
+
+	while ((c = getopt(argc, argv, "f:")) != -1) {
+		switch (c) {
+		case 'f':
+			period = atol(optarg);
+			if (period <= 0)
+				return (1);
+			break;
+		default:
+			return (1);
+		}
+	}
+
+	enumerate_irqs();
+	while (true) {
+		irqshuffle();
+		sleep(period);
+	}
+	/* NOTREACHED */
+	return (0);
+}
+
+static size_t
+read_intrcnts(unsigned long **intrcnts)
+{
+	size_t intrcntlen;
+	int rc;
+
+	for (*intrcnts = NULL, intrcntlen = 1024; ; intrcntlen *= 2) {
+		*intrcnts = reallocf(*intrcnts, intrcntlen);
+		if (*intrcnts == NULL)
+			err(1, "reallocf");
+		rc = sysctlbyname("hw.intrcnt", *intrcnts, &intrcntlen, NULL, 0);
+		if (rc == 0)
+			break;
+		else if (rc != ENOMEM)
+			err(1, "sysctl");
+	}
+
+	return (intrcntlen / sizeof(unsigned long));
+}
+
+static void
+enumerate_irqs(void)
+{
+	size_t inamlen, intrcnt, i;
+	unsigned long *counts;
+	const char *name;
+	int rc;
+
+	for (intrnames = NULL, inamlen = 1024; ; inamlen *= 2) {
+		if ((intrnames = reallocf(intrnames, inamlen)) == NULL)
+			err(1, "reallocf");
+		rc = sysctlbyname("hw.intrnames", intrnames, &inamlen, NULL, 0);
+		if (rc == 0)
+			break;
+		else if (rc != ENOMEM)
+			err(1, "sysctl");
+	}
+
+	intrcnt = read_intrcnts(&counts);
+	free(counts);
+
+	intr_sources = calloc(intrcnt, sizeof(*intr_sources));
+	if (intr_sources == NULL)
+		err(1, "calloc");
+
+	for (i = 0, name = intrnames; i < intrcnt; i++) {
+		if (name[0] != '\0')
+			intr_sources[i].is_name = strdup(name);
+		/* XXX */
+		if (strncmp(name, "irq", 3) != 0) {
+			rc = sscanf(name, "irq%d:", &intr_sources[i].is_irq);
+			if (rc < 1)
+				intr_sources[i].is_irq = -1;
+		} else
+			intr_sources[i].is_irq = -1;
+		name += strlen(name) + 1;
+	}
+
+	rc = cpuset_getaffinity(CPU_LEVEL_ROOT, CPU_WHICH_CPUSET, -1,
+	    sizeof(cpus), &cpus);
+	if (rc != 0)
+		err(1, "cpuset_getaffinity");
+}
+
+static int
+intrcmp(const void *one, const void *two)
+{
+	const struct intr_src *i1, *i2;
+
+	i1 = one;
+	i2 = two;
+	if (i1->is_count != 0 && i2->is_count != 0) {
+		if (i1->is_count < i2->is_count)
+			return (-1);
+		else if (i1->is_count == i2->is_count)
+			return (0);
+		return (1);
+	}
+
+	if (i1->is_count != 0)
+		return (1);
+	else if (i2->is_count != 0)
+		return (-1);
+	return (0);
+}
+
+static size_t
+nextcpu(const cpuset_t *allcpus, size_t idx, cpuset_t *output)
+{
+
+	CPU_ZERO(output);
+	while (true) {
+		if (CPU_ISSET(idx, allcpus)) {
+			CPU_SET(idx, output);
+			break;
+		}
+		idx = (idx + 1) % CPU_SETSIZE;
+	}
+	return ((idx + 1) % CPU_SETSIZE);
+}
+
+static void
+irqshuffle(void)
+{
+	const struct intr_src *isrc;
+	unsigned long *intrcnts;
+	size_t current_cpu;
+	ssize_t i, nintrs;
+	cpuset_t mask;
+	int rc;
+
+	nintrs = read_intrcnts(&intrcnts);
+
+	for (i = 0; i < nintrs; i++)
+		intr_sources[i].is_count = intrcnts[i];
+
+	qsort(intr_sources, nintrs, sizeof(*intr_sources), intrcmp);
+
+	/*
+	 * Scan from the same location to avoid moving in the common case.
+	 */
+	current_cpu = 0;
+
+	for (i = nintrs - 1; i >= 0; i--) {
+		isrc = &intr_sources[i];
+		current_cpu = nextcpu(&cpus, current_cpu, &mask);
+
+		if (isrc->is_irq < 0)
+			continue;
+
+		/* XXX Differentiate managed and unmanaged irqs? */
+		rc = cpuset_setaffinity(CPU_LEVEL_WHICH, CPU_WHICH_IRQ_ONLY,
+		    isrc->is_irq, sizeof(mask), &mask);
+		if (rc != 0)
+			err(1, "cpuset_setaffinity");
+	}
+}
Index: share/mk/src.opts.mk
===================================================================
--- share/mk/src.opts.mk
+++ share/mk/src.opts.mk
@@ -112,6 +112,7 @@
     INETD \
     IPFILTER \
     IPFW \
+    IRQREBALANCE \
     ISCSI \
     JAIL \
     KDUMP \