linux-kernel - [tip:x86/pti] x86/Kconfig: Select SCHED

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Date:   Wed, 28 Nov 2018 06:24:59 -0800
From:   tip-bot for Thomas Gleixner <tipbot@...or.com>
To:     linux-tip-commits@...r.kernel.org
Cc:     keescook@...omium.org, ak@...ux.intel.com, tglx@...utronix.de,
        linux-kernel@...r.kernel.org, casey.schaufler@...el.com,
        asit.k.mallick@...el.com, jcm@...hat.com, mingo@...nel.org,
        dave.hansen@...el.com, gregkh@...uxfoundation.org, luto@...nel.org,
        aarcange@...hat.com, jkosina@...e.cz,
        torvalds@...ux-foundation.org, longman9394@...il.com,
        dwmw@...zon.co.uk, hpa@...or.com, david.c.stewart@...el.com,
        arjan@...ux.intel.com, jpoimboe@...hat.com, peterz@...radead.org,
        thomas.lendacky@....com, tim.c.chen@...ux.intel.com
Subject: [tip:x86/pti] x86/Kconfig: Select SCHED_SMT if SMP enabled

Commit-ID:  dbe733642e01dd108f71436aaea7b328cb28fd87
Gitweb:     https://git.kernel.org/tip/dbe733642e01dd108f71436aaea7b328cb28fd87
Author:     Thomas Gleixner <tglx@...utronix.de>
AuthorDate: Sun, 25 Nov 2018 19:33:37 +0100
Committer:  Thomas Gleixner <tglx@...utronix.de>
CommitDate: Wed, 28 Nov 2018 11:57:07 +0100

x86/Kconfig: Select SCHED_SMT if SMP enabled

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
key.

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 <tglx@...utronix.de>
Reviewed-by: Ingo Molnar <mingo@...nel.org>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Andy Lutomirski <luto@...nel.org>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Jiri Kosina <jkosina@...e.cz>
Cc: Tom Lendacky <thomas.lendacky@....com>
Cc: Josh Poimboeuf <jpoimboe@...hat.com>
Cc: Andrea Arcangeli <aarcange@...hat.com>
Cc: David Woodhouse <dwmw@...zon.co.uk>
Cc: Tim Chen <tim.c.chen@...ux.intel.com>
Cc: Andi Kleen <ak@...ux.intel.com>
Cc: Dave Hansen <dave.hansen@...el.com>
Cc: Casey Schaufler <casey.schaufler@...el.com>
Cc: Asit Mallick <asit.k.mallick@...el.com>
Cc: Arjan van de Ven <arjan@...ux.intel.com>
Cc: Jon Masters <jcm@...hat.com>
Cc: Waiman Long <longman9394@...il.com>
Cc: Greg KH <gregkh@...uxfoundation.org>
Cc: Dave Stewart <david.c.stewart@...el.com>
Cc: Kees Cook <keescook@...omium.org>
Cc: stable@...r.kernel.org
Link: https://lkml.kernel.org/r/20181125185004.337452245@linutronix.de


---
 arch/x86/Kconfig | 8 +-------
 1 file changed, 1 insertion(+), 7 deletions(-)

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index b5286ad2a982..8689e794a43c 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -1000,13 +1000,7 @@ config NR_CPUS
 	  to the kernel image.
 
 config SCHED_SMT
-	bool "SMT (Hyperthreading) scheduler support"
-	depends on SMP
-	---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