linux-kernel - [PATCH 3.16 41/86] x86/Kconfig: Select SCHED

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Date:   Thu, 16 May 2019 16:55:33 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Arjan van de Ven" <arjan@...ux.intel.com>,
        "Andrea Arcangeli" <aarcange@...hat.com>,
        "Tim Chen" <tim.c.chen@...ux.intel.com>,
        "Andy Lutomirski" <luto@...nel.org>,
        "Casey Schaufler" <casey.schaufler@...el.com>,
        "Waiman Long" <longman9394@...il.com>,
        "Dave Stewart" <david.c.stewart@...el.com>,
        "Linus Torvalds" <torvalds@...ux-foundation.org>,
        "Jon Masters" <jcm@...hat.com>,
        "Josh Poimboeuf" <jpoimboe@...hat.com>,
        "Greg KH" <gregkh@...uxfoundation.org>,
        "Tom Lendacky" <thomas.lendacky@....com>,
        "Peter Zijlstra" <peterz@...radead.org>,
        "Jiri Kosina" <jkosina@...e.cz>,
        "David Woodhouse" <dwmw@...zon.co.uk>,
        "Asit Mallick" <asit.k.mallick@...el.com>,
        "Kees Cook" <keescook@...omium.org>,
        "Thomas Gleixner" <tglx@...utronix.de>,
        "Ingo Molnar" <mingo@...nel.org>,
        "Andi Kleen" <ak@...ux.intel.com>,
        "Dave Hansen" <dave.hansen@...el.com>
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 <tglx@...utronix.de>

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
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>
Link: https://lkml.kernel.org/r/20181125185004.337452245@linutronix.de
[bwh: Backported to 3.16: CONFIG_SCHED_SMT depended on CONFG_X86_HT, but that
 also follows CONFIG_SMP]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 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