diff --git a/sys/conf/NOTES b/sys/conf/NOTES
index 94311c61cfda..b84d0c535b14 100644
--- a/sys/conf/NOTES
+++ b/sys/conf/NOTES
@@ -432,7 +432,10 @@ options 	KTRACE_REQUEST_POOL=101
 # defined by the KTR_* constants in <sys/ktr.h>.  KTR_MASK defines the
 # initial value of the ktr_mask variable which determines at runtime
 # what events to trace.  KTR_CPUMASK determines which CPU's log
-# events, with bit X corresponding to CPU X.  KTR_VERBOSE enables
+# events, with bit X corresponding to CPU X.  The layout of the string
+# passed as KTR_CPUMASK must match a serie of bitmasks each of them
+# separated by the ", " characters (ie:
+# KTR_CPUMASK=("0xAF, 0xFFFFFFFFFFFFFFFF")).  KTR_VERBOSE enables
 # dumping of KTR events to the console by default.  This functionality
 # can be toggled via the debug.ktr_verbose sysctl and defaults to off
 # if KTR_VERBOSE is not defined.  See ktr(4) and ktrdump(8) for details.
@@ -441,7 +444,7 @@ options 	KTR
 options 	KTR_ENTRIES=1024
 options 	KTR_COMPILE=(KTR_INTR|KTR_PROC)
 options 	KTR_MASK=KTR_INTR
-options 	KTR_CPUMASK=0x3
+options 	KTR_CPUMASK=("0x3")
 options 	KTR_VERBOSE
 
 #
diff --git a/sys/kern/kern_cpuset.c b/sys/kern/kern_cpuset.c
index 3b2c653de9ef..e1f2801643ac 100644
--- a/sys/kern/kern_cpuset.c
+++ b/sys/kern/kern_cpuset.c
@@ -50,6 +50,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/cpuset.h>
 #include <sys/sx.h>
 #include <sys/queue.h>
+#include <sys/libkern.h>
 #include <sys/limits.h>
 #include <sys/bus.h>
 #include <sys/interrupt.h>
@@ -659,6 +660,43 @@ cpusetobj_strprint(char *buf, const cpuset_t *set)
 	return (buf);
 }
 
+/*
+ * Build a valid cpuset_t object from a string representation.
+ * It expects an incoming buffer at least sized as CPUSETBUFSIZ.
+ */
+int
+cpusetobj_strscan(cpuset_t *set, const char *buf)
+{
+	u_int nwords;
+	int i, ret;
+
+	if (strlen(buf) > CPUSETBUFSIZ - 1)
+		return (-1);
+
+	/* Allow to pass a shorter version of the mask when necessary. */
+	nwords = 1;
+	for (i = 0; buf[i] != '\0'; i++)
+		if (buf[i] == ',')
+			nwords++;
+	if (nwords > _NCPUWORDS)
+		return (-1);
+
+	CPU_ZERO(set);
+	for (i = nwords - 1; i > 0; i--) {
+		ret = sscanf(buf, "%lx, ", &set->__bits[i]);
+		if (ret == 0 || ret == -1)
+			return (-1);
+		buf = strstr(buf, " ");
+		if (buf == NULL)
+			return (-1);
+		buf++;
+	}
+	ret = sscanf(buf, "%lx", &set->__bits[0]);
+	if (ret == 0 || ret == -1)
+		return (-1);
+	return (0);
+}
+
 /*
  * Apply an anonymous mask to a single thread.
  */
diff --git a/sys/kern/kern_ktr.c b/sys/kern/kern_ktr.c
index 2e5e06f671b2..eff3d5bd68ab 100644
--- a/sys/kern/kern_ktr.c
+++ b/sys/kern/kern_ktr.c
@@ -40,8 +40,10 @@ __FBSDID("$FreeBSD$");
 #include "opt_alq.h"
 
 #include <sys/param.h>
+#include <sys/queue.h>
 #include <sys/alq.h>
 #include <sys/cons.h>
+#include <sys/cpuset.h>
 #include <sys/kernel.h>
 #include <sys/ktr.h>
 #include <sys/libkern.h>
@@ -68,10 +70,6 @@ __FBSDID("$FreeBSD$");
 #define	KTR_MASK	(0)
 #endif
 
-#ifndef KTR_CPUMASK
-#define	KTR_CPUMASK	(~0)
-#endif
-
 #ifndef KTR_TIME
 #define	KTR_TIME	get_cyclecount()
 #endif
@@ -84,11 +82,6 @@ FEATURE(ktr, "Kernel support for KTR kernel tracing facility");
 
 SYSCTL_NODE(_debug, OID_AUTO, ktr, CTLFLAG_RD, 0, "KTR options");
 
-int	ktr_cpumask = KTR_CPUMASK;
-TUNABLE_INT("debug.ktr.cpumask", &ktr_cpumask);
-SYSCTL_INT(_debug_ktr, OID_AUTO, cpumask, CTLFLAG_RW,
-    &ktr_cpumask, 0, "Bitmask of CPUs on which KTR logging is enabled");
-
 int	ktr_mask = KTR_MASK;
 TUNABLE_INT("debug.ktr.mask", &ktr_mask);
 SYSCTL_INT(_debug_ktr, OID_AUTO, mask, CTLFLAG_RW,
@@ -106,6 +99,54 @@ int	ktr_version = KTR_VERSION;
 SYSCTL_INT(_debug_ktr, OID_AUTO, version, CTLFLAG_RD,
     &ktr_version, 0, "Version of the KTR interface");
 
+cpuset_t ktr_cpumask;
+static char ktr_cpumask_str[CPUSETBUFSIZ];
+TUNABLE_STR("debug.ktr.cpumask", ktr_cpumask_str, sizeof(ktr_cpumask_str));
+
+static void
+ktr_cpumask_initializer(void *dummy __unused)
+{
+
+	CPU_FILL(&ktr_cpumask);
+#ifdef KTR_CPUMASK
+	if (cpusetobj_strscan(&ktr_cpumask, KTR_CPUMASK) == -1)
+		CPU_FILL(&ktr_cpumask);
+#endif
+
+	/*
+	 * TUNABLE_STR() runs with SI_ORDER_MIDDLE priority, thus it must be
+	 * already set, if necessary.
+	 */
+	if (ktr_cpumask_str[0] != '\0' &&
+	    cpusetobj_strscan(&ktr_cpumask, ktr_cpumask_str) == -1)
+		CPU_FILL(&ktr_cpumask);
+}
+SYSINIT(ktr_cpumask_initializer, SI_SUB_TUNABLES, SI_ORDER_ANY,
+    ktr_cpumask_initializer, NULL);
+
+static int
+sysctl_debug_ktr_cpumask(SYSCTL_HANDLER_ARGS)
+{
+	char lktr_cpumask_str[CPUSETBUFSIZ];
+	cpuset_t imask;
+	int error;
+
+	cpusetobj_strprint(lktr_cpumask_str, &ktr_cpumask);
+	error = sysctl_handle_string(oidp, lktr_cpumask_str,
+	    sizeof(lktr_cpumask_str), req);
+	if (error != 0 || req->newptr == NULL)
+		return (error);
+	if (cpusetobj_strscan(&imask, lktr_cpumask_str) == -1)
+		return (EINVAL);
+	CPU_COPY(&imask, &ktr_cpumask);
+
+	return (error);
+}
+SYSCTL_PROC(_debug_ktr, OID_AUTO, cpumask,
+    CTLFLAG_RW | CTLFLAG_MPSAFE | CTLTYPE_STRING, NULL, 0,
+    sysctl_debug_ktr_cpumask, "S",
+    "Bitmask of CPUs on which KTR logging is enabled");
+
 volatile int	ktr_idx = 0;
 struct	ktr_entry ktr_buf[KTR_ENTRIES];
 
@@ -213,7 +254,7 @@ ktr_tracepoint(u_int mask, const char *file, int line, const char *format,
 	if ((ktr_mask & mask) == 0)
 		return;
 	cpu = KTR_CPU;
-	if (((1 << cpu) & ktr_cpumask) == 0)
+	if (!CPU_ISSET(cpu, &ktr_cpumask))
 		return;
 #if defined(KTR_VERBOSE) || defined(KTR_ALQ)
 	td = curthread;
diff --git a/sys/sparc64/include/ktr.h b/sys/sparc64/include/ktr.h
index 5948ba29fb3e..2a9966b7ce9c 100644
--- a/sys/sparc64/include/ktr.h
+++ b/sys/sparc64/include/ktr.h
@@ -85,7 +85,9 @@ l2:	add	r2, 1, r3 ; \
 	lduw	[PCPU(MID)], r1 ; \
 	mov	1, r2 ; \
 	sllx	r2, r1, r1 ; \
+#ifdef notyet \
 	TEST(ktr_cpumask, r1, r2, r3, l3) ; \
+#endif \
 	ATR(desc, r1, r2, r3, l1, l2)
 
 #endif /* LOCORE */
diff --git a/sys/sys/cpuset.h b/sys/sys/cpuset.h
index 45252638e15a..030a874bf7d4 100644
--- a/sys/sys/cpuset.h
+++ b/sys/sys/cpuset.h
@@ -214,6 +214,7 @@ int	cpuset_create_root(struct prison *, struct cpuset **);
 int	cpuset_setproc_update_set(struct proc *, struct cpuset *);
 int	cpusetobj_ffs(const cpuset_t *);
 char	*cpusetobj_strprint(char *, const cpuset_t *);
+int	cpusetobj_strscan(cpuset_t *, const char *);
 
 #else
 __BEGIN_DECLS
diff --git a/sys/sys/ktr.h b/sys/sys/ktr.h
index 3b78101dd1b4..7885b22f4aee 100644
--- a/sys/sys/ktr.h
+++ b/sys/sys/ktr.h
@@ -97,6 +97,9 @@
 
 #ifndef LOCORE
 
+#include <sys/param.h>
+#include <sys/_cpuset.h>
+
 struct ktr_entry {
 	u_int64_t ktr_timestamp;
 	int	ktr_cpu;
@@ -107,7 +110,7 @@ struct ktr_entry {
 	u_long	ktr_parms[KTR_PARMS];
 };
 
-extern int ktr_cpumask;
+extern cpuset_t ktr_cpumask;
 extern int ktr_mask;
 extern int ktr_entries;
 extern int ktr_verbose;