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Date:   Thu, 16 May 2019 16:55:33 +0100
From:   Ben Hutchings <>
CC:, Denis Kirjanov <>,
        "Arjan van de Ven" <>,
        "Andrea Arcangeli" <>,
        "Tim Chen" <>,
        "Andy Lutomirski" <>,
        "Casey Schaufler" <>,
        "Waiman Long" <>,
        "Dave Stewart" <>,
        "Linus Torvalds" <>,
        "Jon Masters" <>,
        "Josh Poimboeuf" <>,
        "Greg KH" <>,
        "Tom Lendacky" <>,
        "Peter Zijlstra" <>,
        "Jiri Kosina" <>,
        "David Woodhouse" <>,
        "Asit Mallick" <>,
        "Kees Cook" <>,
        "Thomas Gleixner" <>,
        "Ingo Molnar" <>,
        "Andi Kleen" <>,
        "Dave Hansen" <>
Subject: [PATCH 3.16 41/86] x86/Kconfig: Select SCHED_SMT if SMP enabled

3.16.68-rc1 review patch.  If anyone has any objections, please let me know.


From: Thomas Gleixner <>

commit dbe733642e01dd108f71436aaea7b328cb28fd87 upstream.

CONFIG_SCHED_SMT is enabled by all distros, so there is not a real point to
have it configurable. The runtime overhead in the core scheduler code is
minimal because the actual SMT scheduling parts are conditional on a static

This allows to expose the scheduler's SMT state static key to the
speculation control code. Alternatively the scheduler's static key could be
made always available when CONFIG_SMP is enabled, but that's just adding an
unused static key to every other architecture for nothing.

Signed-off-by: Thomas Gleixner <>
Reviewed-by: Ingo Molnar <>
Cc: Peter Zijlstra <>
Cc: Andy Lutomirski <>
Cc: Linus Torvalds <>
Cc: Jiri Kosina <>
Cc: Tom Lendacky <>
Cc: Josh Poimboeuf <>
Cc: Andrea Arcangeli <>
Cc: David Woodhouse <>
Cc: Tim Chen <>
Cc: Andi Kleen <>
Cc: Dave Hansen <>
Cc: Casey Schaufler <>
Cc: Asit Mallick <>
Cc: Arjan van de Ven <>
Cc: Jon Masters <>
Cc: Waiman Long <>
Cc: Greg KH <>
Cc: Dave Stewart <>
Cc: Kees Cook <>
[bwh: Backported to 3.16: CONFIG_SCHED_SMT depended on CONFG_X86_HT, but that
 also follows CONFIG_SMP]
Signed-off-by: Ben Hutchings <>
 arch/x86/Kconfig | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -798,13 +798,7 @@ config NR_CPUS
 	  approximately eight kilobytes to the kernel image.
 config SCHED_SMT
-	bool "SMT (Hyperthreading) scheduler support"
-	depends on X86_HT
-	---help---
-	  SMT scheduler support improves the CPU scheduler's decision making
-	  when dealing with Intel Pentium 4 chips with HyperThreading at a
-	  cost of slightly increased overhead in some places. If unsure say
-	  N here.
+	def_bool y if SMP
 config SCHED_MC
 	def_bool y

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