diff --git a/lib/libc/sys/sysctl.2 b/lib/libc/sys/sysctl.2
index ce4da218d63..a0d3dd438ae 100644
--- a/lib/libc/sys/sysctl.2
+++ b/lib/libc/sys/sysctl.2
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: sysctl.2,v 1.70 2025/09/16 09:19:43 florian Exp $
+.\"	$OpenBSD: sysctl.2,v 1.71 2026/03/31 16:46:22 deraadt Exp $
 .\"
 .\" Copyright (c) 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -27,7 +27,7 @@
 .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 .\" SUCH DAMAGE.
 .\"
-.Dd $Mdocdate: September 16 2025 $
+.Dd $Mdocdate: March 31 2026 $
 .Dt SYSCTL 2
 .Os
 .Sh NAME
@@ -274,6 +274,7 @@ privileges may change the value.
 .It Dv HW_SETPERF Ta "integer" Ta "yes"
 .It Dv HW_SMT Ta "integer" Ta "yes"
 .It Dv HW_UCOMNAMES Ta "string" Ta "no"
+.It Dv HW_BLOCKCPU Ta "string" Ta "yes"
 .It Dv HW_USERMEM Ta "integer" Ta "no"
 .It Dv HW_USERMEM64 Ta "int64_t" Ta "no"
 .It Dv HW_UUID Ta "string" Ta "no"
@@ -421,7 +422,21 @@ is set to
 .It Dv HW_SMT Pq Va hw.smt
 If set to 1, enable simultaneous multithreading (SMT) on CPUs that
 support it.
-Disabled by default.
+Deprecated, use
+.Va hw.blockcpu
+instead.
+.It Dv HW_BLOCKCPU Pq Va hw.smt
+A series of characters
+.Ar ( S
+(SMT),
+.Ar P
+(Performance core),
+.Ar E
+(Efficiency core),
+and
+.Ar L
+(Lethargic, Low Power Efficiency core)
+representing cpu types to avoid schedule tasks onto.
 .It Dv HW_UCOMNAMES Pq Va hw.ucomnames
 A comma-separated list of currently attached
 .Xr ucom 4
diff --git a/sys/arch/amd64/amd64/identcpu.c b/sys/arch/amd64/amd64/identcpu.c
index ac4e845a1aa..527a199a3ee 100644
--- a/sys/arch/amd64/amd64/identcpu.c
+++ b/sys/arch/amd64/amd64/identcpu.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: identcpu.c,v 1.152 2025/09/14 15:52:28 mlarkin Exp $	*/
+/*	$OpenBSD: identcpu.c,v 1.153 2026/03/31 16:46:22 deraadt Exp $	*/
 /*	$NetBSD: identcpu.c,v 1.1 2003/04/26 18:39:28 fvdl Exp $	*/
 
 /*
@@ -831,6 +831,7 @@ cpu_topology(struct cpu_info *ci)
 	u_int32_t apicid, max_apicid = 0, max_coreid = 0;
 	u_int32_t smt_bits = 0, core_bits, pkg_bits = 0;
 	u_int32_t smt_mask = 0, core_mask, pkg_mask = 0;
+	char type[8], *typ = type;
 
 	/* We need at least apicid at CPUID 1 */
 	if (ci->ci_cpuid_level < 1)
@@ -865,7 +866,10 @@ cpu_topology(struct cpu_info *ci)
 
 		/* Cut logical thread_id into core id, and smt id in a core */
 		ci->ci_core_id = thread_id / nthreads;
-		ci->ci_smt_id = thread_id % nthreads;
+		if (ci->ci_smt_id) {
+			ci->ci_cputype |= CPUTYP_SMT;
+			*typ++ = 'S';
+		}
 	} else if (ci->ci_vendor == CPUV_INTEL) {
 		/* We only support leaf 1/4 detection */
 		if (ci->ci_cpuid_level < 4)
@@ -888,10 +892,36 @@ cpu_topology(struct cpu_info *ci)
 		pkg_mask = ~0U << core_bits;
 
 		ci->ci_smt_id = apicid & smt_mask;
+		if (ci->ci_smt_id) {
+			ci->ci_cputype |= CPUTYP_SMT;
+			*typ++ = 'S';
+		}
 		ci->ci_core_id = (apicid & core_mask) >> smt_bits;
 		ci->ci_pkg_id = (apicid & pkg_mask) >> pkg_bits;
+
+		if (ci->ci_cpuid_level >= 0x1a) {
+			CPUID_LEAF(0x1a, 0, eax, ebx, ecx, edx);
+			if ((eax >> 24) == 0x20) {
+				CPUID_LEAF(4, 3, eax, ebx, ecx, edx);
+				if (eax == 0) {
+					/* No L3 cache is classified as Lethargic */
+					ci->ci_cputype |= CPUTYP_L;
+					*typ++ = 'L';
+				} else {
+					ci->ci_cputype |= CPUTYP_E;
+					*typ++ = 'E';
+				}
+			}
+		}
+	
 	} else
 		goto no_topology;
+	if ((ci->ci_cputype & (CPUTYP_E | CPUTYP_L)) == 0) {
+		ci->ci_cputype |= CPUTYP_P;
+		*typ++ = 'P';
+	}
+	*typ ='\0';
+
 #ifdef DEBUG
 	printf("cpu%d: smt %u, core %u, pkg %u "
 		"(apicid 0x%x, max_apicid 0x%x, max_coreid 0x%x, smt_bits 0x%x, smt_mask 0x%x, "
@@ -900,14 +930,15 @@ cpu_topology(struct cpu_info *ci)
 		apicid, max_apicid, max_coreid, smt_bits, smt_mask, core_bits,
 		core_mask, pkg_bits, pkg_mask);
 #else
-	printf("cpu%d: smt %u, core %u, package %u\n", ci->ci_cpuid,
-		ci->ci_smt_id, ci->ci_core_id, ci->ci_pkg_id);
+	printf("cpu%d: smt %u, core %u, package %u, type %s\n", ci->ci_cpuid,
+		ci->ci_smt_id, ci->ci_core_id, ci->ci_pkg_id, type);
 
 #endif
 	return;
 	/* We can't map, so consider ci_core_id as ci_cpuid */
 no_topology:
 #endif
+	ci->ci_cputype = CPUTYP_P;
 	ci->ci_smt_id  = 0;
 	ci->ci_core_id = ci->ci_cpuid;
 	ci->ci_pkg_id  = 0;
diff --git a/sys/arch/amd64/amd64/machdep.c b/sys/arch/amd64/amd64/machdep.c
index 33bb4dfc47b..98eddde4ab0 100644
--- a/sys/arch/amd64/amd64/machdep.c
+++ b/sys/arch/amd64/amd64/machdep.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: machdep.c,v 1.307 2026/03/11 16:18:42 kettenis Exp $	*/
+/*	$OpenBSD: machdep.c,v 1.308 2026/03/31 16:46:22 deraadt Exp $	*/
 /*	$NetBSD: machdep.c,v 1.3 2003/05/07 22:58:18 fvdl Exp $	*/
 
 /*-
@@ -1483,6 +1483,8 @@ init_x86_64(paddr_t first_avail)
 	int x, ist;
 	uint64_t max_dm_size = ((uint64_t)512 * NUM_L4_SLOT_DIRECT) << 30;
 
+	sched_blockcpu = CPUTYP_SMT | CPUTYP_L;
+
 	/*
 	 * locore0 mapped 2 pages for use as GHCB before pmap is initialized.
 	 */
diff --git a/sys/arch/amd64/include/cpu.h b/sys/arch/amd64/include/cpu.h
index c0df3670517..15423f5d5f2 100644
--- a/sys/arch/amd64/include/cpu.h
+++ b/sys/arch/amd64/include/cpu.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: cpu.h,v 1.184 2026/03/11 16:18:42 kettenis Exp $	*/
+/*	$OpenBSD: cpu.h,v 1.185 2026/03/31 16:46:22 deraadt Exp $	*/
 /*	$NetBSD: cpu.h,v 1.1 2003/04/26 18:39:39 fvdl Exp $	*/
 
 /*-
@@ -188,6 +188,7 @@ struct cpu_info {
 	int		ci_inatomic;		/* [o] */
 
 #define __HAVE_CPU_TOPOLOGY
+	u_int32_t	ci_cputype;		/* [I] */
 	u_int32_t	ci_smt_id;		/* [I] */
 	u_int32_t	ci_core_id;		/* [I] */
 	u_int32_t	ci_pkg_id;		/* [I] */
diff --git a/sys/kern/kern_sched.c b/sys/kern/kern_sched.c
index 74183e6bb68..ead659aafb5 100644
--- a/sys/kern/kern_sched.c
+++ b/sys/kern/kern_sched.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_sched.c,v 1.113 2025/06/12 20:37:58 deraadt Exp $	*/
+/*	$OpenBSD: kern_sched.c,v 1.114 2026/03/31 16:46:22 deraadt Exp $	*/
 /*
  * Copyright (c) 2007, 2008 Artur Grabowski <art@openbsd.org>
  *
@@ -54,8 +54,9 @@ uint64_t sched_stolen;		/* Times we stole proc from other cpus */
 uint64_t sched_choose;		/* Times we chose a cpu */
 uint64_t sched_wasidle;		/* Times we came out of idle */
 
-/* Only schedule processes on sibling CPU threads when true. */
-int sched_smt;
+#ifdef __HAVE_CPU_TOPOLOGY
+int sched_blockcpu;		/* Types of cpu to not schedule on */
+#endif
 
 /*
  * A few notes about cpu_switchto that is implemented in MD code.
@@ -153,7 +154,7 @@ sched_idle(void *v)
 	 * After that just go away and properly reenter once idle.
 	 */
 #ifdef __HAVE_CPU_TOPOLOGY
-	if (sched_smt || ci->ci_smt_id == 0)
+	if ((ci->ci_cputype & sched_blockcpu) == 0)
 		cpuset_add(&sched_all_cpus, ci);
 #else
 	cpuset_add(&sched_all_cpus, ci);
@@ -659,7 +660,7 @@ sched_start_secondary_cpus(void)
 		atomic_clearbits_int(&spc->spc_schedflags,
 		    SPCF_SHOULDHALT | SPCF_HALTED);
 #ifdef __HAVE_CPU_TOPOLOGY
-		if (!sched_smt && ci->ci_smt_id > 0)
+		if (ci->ci_cputype & sched_blockcpu)
 			continue;
 #endif
 		cpuset_add(&sched_all_cpus, ci);
@@ -847,33 +848,108 @@ cpu_is_online(struct cpu_info *ci)
 
 #ifndef SMALL_KERNEL
 int
-sysctl_hwsmt(void *oldp, size_t *oldlenp, void *newp, size_t newlen)
+sched_cpuadjust(int newblockcpu)
 {
 	CPU_INFO_ITERATOR cii;
 	struct cpu_info *ci;
-	int err, newsmt;
+	int inset;
 
-	newsmt = sched_smt;
-	err = sysctl_int_bounded(oldp, oldlenp, newp, newlen, &newsmt, 0, 1);
-	if (err)
-		return err;
-	if (newsmt == sched_smt)
+	if (newblockcpu == sched_blockcpu)
 		return 0;
-
-	sched_smt = newsmt;
+	sched_blockcpu = newblockcpu;
 	CPU_INFO_FOREACH(cii, ci) {
 		if (CPU_IS_PRIMARY(ci) || !CPU_IS_RUNNING(ci))
 			continue;
-		if (ci->ci_smt_id == 0)
-			continue;
-		if (sched_smt)
-			cpuset_add(&sched_all_cpus, ci);
-		else
-			cpuset_del(&sched_all_cpus, ci);
+		inset = cpuset_isset(&sched_all_cpus, ci);
+		if (ci->ci_cputype & sched_blockcpu) {
+			if (inset)
+				cpuset_del(&sched_all_cpus, ci);
+		} else {
+			if (!inset)
+				cpuset_add(&sched_all_cpus, ci);
+		}
 	}
-
 	return 0;
 }
+
+/* emulate hw.smt temporarily */
+int
+sysctl_hwsmt(void *oldp, size_t *oldlenp, void *newp, size_t newlen)
+{
+	int err, newsmt = 1, newblockcpu = 0;
+
+#ifdef CPUTYP_SMT
+	if (sched_blockcpu & CPUTYP_SMT)
+		newsmt = 0;
+#endif
+	err = sysctl_int_bounded(oldp, oldlenp, newp, newlen, &newsmt, 0, 1);
+	if (err || newp == NULL)
+		return err;
+#ifdef CPUTYP_SMT
+	if (newsmt)
+		newblockcpu &= ~CPUTYP_SMT;
+#endif
+	return sched_cpuadjust(newblockcpu);
+} 
+
+int
+sysctl_hwblockcpu(void *oldp, size_t *oldlenp, void *newp, size_t newlen)
+{
+	int err, newblockcpu;
+	char type[8], *typ = type;
+
+#ifdef CPUTYP_SMT
+	if (sched_blockcpu & CPUTYP_SMT)
+		*typ++ = 'S';
+#endif
+#ifdef CPUTYP_P
+	if (sched_blockcpu & CPUTYP_P)
+		*typ++ = 'P';
+#endif
+#ifdef CPUTYP_E
+	if (sched_blockcpu & CPUTYP_E)
+		*typ++ = 'E';
+#endif
+#ifdef CPUTYP_L
+	if (sched_blockcpu & CPUTYP_L)
+		*typ++ = 'L';
+#endif
+	*typ = '\0';
+	if (newp == NULL)
+		return sysctl_rdstring(oldp, oldlenp, newp, type);
+
+	err = sysctl_string(oldp, oldlenp, newp, newlen, type, sizeof type);
+	if (err)
+		return err;
+	for (newblockcpu = 0, typ = type; *typ; typ++) {
+		switch (*typ) {
+#ifdef CPUTYP_SMT
+		case 'S':
+			newblockcpu |= CPUTYP_SMT;
+			break;
+#endif
+#ifdef CPUTYP_P
+		case 'P':
+			newblockcpu |= CPUTYP_P;
+			break;
+#endif
+#ifdef CPUTYP_P
+		case 'E':
+			newblockcpu |= CPUTYP_E;
+			break;
+#endif
+#ifdef CPUTYP_P
+		case 'L':
+			newblockcpu |= CPUTYP_L;
+			break;
+#endif
+		default:
+			return (EINVAL);
+		}
+	}
+	return sched_cpuadjust(newblockcpu);
+}
+
 #endif /* SMALL_KERNEL */
 
 #endif /* __HAVE_CPU_TOPOLOGY */
diff --git a/sys/kern/kern_sysctl.c b/sys/kern/kern_sysctl.c
index e196df44620..d15f359dc0e 100644
--- a/sys/kern/kern_sysctl.c
+++ b/sys/kern/kern_sysctl.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: kern_sysctl.c,v 1.486 2026/03/25 05:05:41 deraadt Exp $	*/
+/*	$OpenBSD: kern_sysctl.c,v 1.487 2026/03/31 16:46:22 deraadt Exp $	*/
 /*	$NetBSD: kern_sysctl.c,v 1.17 1996/05/20 17:49:05 mrg Exp $	*/
 
 /*-
@@ -884,6 +884,7 @@ hw_sysctl(int *name, u_int namelen, void *oldp, size_t *oldlenp, void *newp,
 	case HW_UCOMNAMES:
 #ifdef __HAVE_CPU_TOPOLOGY
 	case HW_SMT:
+	case HW_BLOCKCPU:
 #endif
 #endif /* !SMALL_KERNEL */
 	{
@@ -984,6 +985,8 @@ hw_sysctl_locked(int *name, u_int namelen, void *oldp, size_t *oldlenp,
 #ifdef __HAVE_CPU_TOPOLOGY
 	case HW_SMT:
 		return (sysctl_hwsmt(oldp, oldlenp, newp, newlen));
+	case HW_BLOCKCPU:
+		return (sysctl_hwblockcpu(oldp, oldlenp, newp, newlen));
 #endif
 	case HW_BATTERY:
 		return (sysctl_hwbattery(name + 1, namelen - 1, oldp, oldlenp,
diff --git a/sys/sys/sched.h b/sys/sys/sched.h
index 64c7044204c..6814a6bbd6b 100644
--- a/sys/sys/sched.h
+++ b/sys/sys/sched.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: sched.h,v 1.77 2025/06/09 10:57:46 claudio Exp $	*/
+/*	$OpenBSD: sched.h,v 1.78 2026/03/31 16:46:21 deraadt Exp $	*/
 /* $NetBSD: sched.h,v 1.2 1999/02/28 18:14:58 ross Exp $ */
 
 /*-
@@ -179,8 +179,15 @@ void sched_barrier(struct cpu_info *ci);
 int sysctl_hwsetperf(void *, size_t *, void *, size_t);
 int sysctl_hwperfpolicy(void *, size_t *, void *, size_t);
 int sysctl_hwsmt(void *, size_t *, void *, size_t);
+int sysctl_hwblockcpu(void *, size_t *, void *, size_t);
 int sysctl_hwncpuonline(void);
 
+#define CPUTYP_SMT	0x01	/* SMT cpu */
+#define CPUTYP_P	0x02	/* Performance core */
+#define CPUTYP_E	0x04	/* Efficiency core */
+#define CPUTYP_L	0x08	/* Lethargic, Low Power Efficiency core */
+extern int sched_blockcpu;
+
 #ifdef MULTIPROCESSOR
 void sched_start_secondary_cpus(void);
 void sched_stop_secondary_cpus(void);
diff --git a/sys/sys/sysctl.h b/sys/sys/sysctl.h
index 5dd7eebfa38..90682f2c80d 100644
--- a/sys/sys/sysctl.h
+++ b/sys/sys/sysctl.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: sysctl.h,v 1.246 2025/07/31 09:05:11 mvs Exp $	*/
+/*	$OpenBSD: sysctl.h,v 1.247 2026/03/31 16:46:21 deraadt Exp $	*/
 /*	$NetBSD: sysctl.h,v 1.16 1996/04/09 20:55:36 cgd Exp $	*/
 
 /*
@@ -926,7 +926,8 @@ struct kinfo_file {
 #define	HW_POWER		26	/* int: machine has wall-power */
 #define	HW_BATTERY		27	/* node: battery */
 #define	HW_UCOMNAMES		28	/* strings: ucom names */
-#define	HW_MAXID		29	/* number of valid hw ids */
+#define	HW_BLOCKCPU		29	/* string: cpu types to block */
+#define	HW_MAXID		30	/* number of valid hw ids */
 
 #define	CTL_HW_NAMES { \
 	{ 0, 0 }, \
@@ -958,6 +959,7 @@ struct kinfo_file {
 	{ "power", CTLTYPE_INT }, \
 	{ "battery", CTLTYPE_NODE }, \
 	{ "ucomnames", CTLTYPE_STRING }, \
+	{ "blockcpu", CTLTYPE_STRING }, \
 }
 
 /*