Index: share/man/man4/smp.4
===================================================================
--- share/man/man4/smp.4
+++ share/man/man4/smp.4
@@ -23,7 +23,7 @@
 .\"
 .\" $FreeBSD$
 .\"
-.Dd January 6, 2018
+.Dd November 23, 2018
 .Dt SMP 4
 .Os
 .Sh NAME
@@ -35,27 +35,6 @@
 The
 .Nm
 kernel implements symmetric multi-processor support.
-.Sh COMPATIBILITY
-Support for multi-processor systems is present for all Tier-1
-architectures on
-.Fx .
-Currently, this includes amd64, i386 and sparc64.
-Support is enabled using
-.Cd options SMP .
-It is permissible to use the SMP kernel configuration on non-SMP equipped
-motherboards.
-.Sh I386 NOTES
-For i386 systems, the
-.Nm
-kernel supports motherboards that follow the Intel MP specification,
-version 1.4.
-In addition to
-.Cd options SMP ,
-i386 also requires
-.Cd device apic .
-The
-.Xr mptable 1
-command may be used to view the status of multi-processor support.
 .Pp
 .Nm
 support can be disabled by setting the loader tunable
@@ -66,6 +45,13 @@
 the read-only sysctl variable
 .Va hw.ncpu .
 .Pp
+The number of threads per CPU core detected by the system is available in the
+read-only sysctl variable
+.Va kern.smp.smt_threads_online .
+The number of physical CPU cores detected by the system is available in the
+read-only sysctl variable
+.Va hw.physicalcpu .
+.Pp
 .Fx
 allows specific CPUs on a multi-processor system to be disabled.
 This can be done using the
@@ -74,6 +60,12 @@
 Setting this tunable to 1 will result in the corresponding CPU being
 disabled.
 .Pp
+.Fx
+supports hyperthreading on the i386 and AMD64 platforms.
+On these platforms, the logical CPUs can be disabled by setting the
+.Va machdep.hyperthreading_allowed
+tunable to zero.
+.Pp
 The
 .Xr sched_ule 4
 scheduler implements CPU topology detection and adjusts the scheduling
@@ -122,13 +114,27 @@
 .Pp
 This information is used internally by the kernel to schedule related
 tasks on CPUs that are closely grouped together.
-.Pp
-.Fx
-supports hyperthreading on Intel CPU's on the i386 and AMD64 platforms.
-Because using logical CPUs can cause performance penalties under certain loads,
-the logical CPUs can be disabled by setting the
-.Va machdep.hyperthreading_allowed
-tunable to zero.
+.Sh COMPATIBILITY
+Support for multi-processor systems is present for all Tier-1
+architectures on
+.Fx .
+Currently, this includes amd64, i386 and sparc64.
+Support is enabled using
+.Cd options SMP .
+It is permissible to use the SMP kernel configuration on non-SMP equipped
+motherboards.
+.Sh I386 NOTES
+For i386 systems, the
+.Nm
+kernel supports motherboards that follow the Intel MP specification,
+version 1.4.
+In addition to
+.Cd options SMP ,
+i386 also requires
+.Cd device apic .
+The
+.Xr mptable 1
+command may be used to view the status of multi-processor support.
 .Sh SEE ALSO
 .Xr cpuset 1 ,
 .Xr mptable 1 ,
@@ -166,3 +172,20 @@
 also introduced support for SMP on the sparc64 architecture.
 .Sh AUTHORS
 .An Steve Passe Aq Mt fsmp@FreeBSD.org
+.Sh CAVEATS
+The
+.Va kern.smp.smt_threads_online
+and
+.Va hw.physicalcpu
+sysctl variables are provided as a best-effort guess.
+If an architecture adds SMT and
+.Fx
+has not yet implemented detection, the reported values may be inaccurate.
+In this case,
+.Va kern.smp.smt_threads_online
+will report
+.Dv 1
+and
+.Va hw.physicalcpu
+will report the same value as
+.Va hw.ncpu .
Index: sys/kern/subr_smp.c
===================================================================
--- sys/kern/subr_smp.c
+++ sys/kern/subr_smp.c
@@ -56,6 +56,9 @@
 #ifdef SMP
 MALLOC_DEFINE(M_TOPO, "toponodes", "SMP topology data");
 
+int cpu_topo_probed = 0;
+struct topo_node topo_root = TOPO_NODE_INITIALIZER(topo_root);
+
 volatile cpuset_t stopped_cpus;
 volatile cpuset_t started_cpus;
 volatile cpuset_t suspended_cpus;
@@ -98,6 +101,14 @@
 SYSCTL_INT(_kern_smp, OID_AUTO, cpus, CTLFLAG_RD|CTLFLAG_CAPRD, &smp_cpus, 0,
     "Number of CPUs online");
 
+int smp_smt_threads_online = 1;	/* how many SMT threads are running per core */
+SYSCTL_INT(_kern_smp, OID_AUTO, smt_threads_online, CTLFLAG_RD|CTLFLAG_CAPRD,
+    &smp_smt_threads_online, 0, "Number of SMT threads online per core");
+
+int smp_cores = 1;	/* how many physical cores running */
+SYSCTL_S32(_hw, OID_AUTO, physicalcpu, CTLFLAG_RD|CTLFLAG_CAPRD, &smp_cores, 0,
+    "Number of physical CPU cores online");
+
 int smp_topology = 0;	/* Which topology we're using. */
 SYSCTL_INT(_kern_smp, OID_AUTO, topology, CTLFLAG_RDTUN, &smp_topology, 0,
     "Topology override setting; 0 is default provided by hardware.");
@@ -149,6 +160,7 @@
 static void
 mp_start(void *dummy)
 {
+	struct topo_analysis topology;
 
 	mtx_init(&smp_ipi_mtx, "smp rendezvous", NULL, MTX_SPIN);
 
@@ -162,7 +174,26 @@
 	cpu_mp_start();
 	printf("FreeBSD/SMP: Multiprocessor System Detected: %d CPUs\n",
 	    mp_ncpus);
+
+	/*
+	 * Best guess, for lack of better information on any given arch.  Allow
+	 * archs to, e.g., override with known information in
+	 * cpu_mp_announce(), without implementing full topology probing.
+	 */
+	smp_cores = mp_ncpus;
+
 	cpu_mp_announce();
+
+	/* Not all arch support probing this MI topology structure yet */
+	if (cpu_topo_probed == 0)
+		return;
+	if (topo_analyze(&topo_root, 0, &topology) == 0)
+		return;
+
+	if (topology.entities[TOPO_LEVEL_THREAD] > 1)
+		smp_smt_threads_online = topology.entities[TOPO_LEVEL_THREAD];
+	if (topology.entities[TOPO_LEVEL_CORE] > 0)
+		smp_cores = topology.entities[TOPO_LEVEL_CORE];
 }
 SYSINIT(cpu_mp, SI_SUB_CPU, SI_ORDER_THIRD, mp_start, NULL);
 
@@ -1140,6 +1171,9 @@
     struct topo_analysis *results)
 {
 
+	KASSERT(cpu_topo_probed,
+	    ("cannot use %s before probing topology", __func__));
+
 	results->entities[TOPO_LEVEL_PKG] = -1;
 	results->entities[TOPO_LEVEL_CORE] = -1;
 	results->entities[TOPO_LEVEL_THREAD] = -1;
Index: sys/sys/param.h
===================================================================
--- sys/sys/param.h
+++ sys/sys/param.h
@@ -60,7 +60,7 @@
  *		in the range 5 to 9.
  */
 #undef __FreeBSD_version
-#define __FreeBSD_version 1300003	/* Master, propagated to newvers */
+#define __FreeBSD_version 1300004	/* Master, propagated to newvers */
 
 /*
  * __FreeBSD_kernel__ indicates that this system uses the kernel of FreeBSD,
Index: sys/sys/smp.h
===================================================================
--- sys/sys/smp.h
+++ sys/sys/smp.h
@@ -62,6 +62,11 @@
 	int					nchildren;
 	int					cpu_count;
 };
+#define TOPO_NODE_INITIALIZER(node)					\
+{									\
+	.children = TAILQ_HEAD_INITIALIZER((node).children),		\
+	.type = TOPO_TYPE_SYSTEM,					\
+}
 
 /*
  * Scheduling topology of a NUMA or SMP system.
@@ -139,6 +144,8 @@
 struct topo_analysis {
 	int entities[TOPO_LEVEL_COUNT];
 };
+extern int cpu_topo_probed;
+extern struct topo_node topo_root;
 int topo_analyze(struct topo_node *topo_root, int all,
     struct topo_analysis *results);
 
Index: sys/x86/x86/mp_x86.c
===================================================================
--- sys/x86/x86/mp_x86.c
+++ sys/x86/x86/mp_x86.c
@@ -147,8 +147,6 @@
 SYSCTL_INT(_machdep, OID_AUTO, hyperthreading_allowed, CTLFLAG_RDTUN,
 	&hyperthreading_allowed, 0, "Use Intel HTT logical CPUs");
 
-static struct topo_node topo_root;
-
 static int pkg_id_shift;
 static int node_id_shift;
 static int core_id_shift;
@@ -487,7 +485,6 @@
 void
 topo_probe(void)
 {
-	static int cpu_topo_probed = 0;
 	struct x86_topo_layer {
 		int type;
 		int subtype;