linux-kernel - [PATCH 2/2] x86: Move x86_cpu_to_apicid to the __read

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Message-Id: <201204171416.45799.vlad@scalemp.com>
Date:	Tue, 17 Apr 2012 14:16:45 +0300
From:	Vlad Zolotarov <vlad@...lemp.com>
To:	"linux-kernel" <linux-kernel@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>
Cc:	"Shai Fultheim (Shai@...leMP.com)" <Shai@...lemp.com>,
	ido@...ery.com
Subject: [PATCH 2/2] x86: Move x86_cpu_to_apicid to the __read_mostly section

From: Shai Fultheim <shai@...lemp.com>

x86_cpu_to_apicid is only written to during initialization. Benchmarks
show that moving it to the __read_mostly section helps avoid false
sharing on large multiprocessing systems.

Signed-off-by: Shai Fultheim <shai@...lemp.com>
Signed-off-by: Vlad Zolotarov <vlad@...lemp.com>
---
 arch/x86/include/asm/smp.h |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
index 0434c40..b9d6c1e 100644
--- a/arch/x86/include/asm/smp.h
+++ b/arch/x86/include/asm/smp.h
@@ -53,7 +53,7 @@ static inline struct cpumask *cpu_llc_shared_mask(int cpu)
 	return per_cpu(cpu_llc_shared_map, cpu);
 }
 
-DECLARE_EARLY_PER_CPU(u16, x86_cpu_to_apicid);
+DECLARE_EARLY_PER_CPU_READ_MOSTLY(u16, x86_cpu_to_apicid);
 DECLARE_EARLY_PER_CPU(u16, x86_bios_cpu_apicid);
 #if defined(CONFIG_X86_LOCAL_APIC) && defined(CONFIG_X86_32)
 DECLARE_EARLY_PER_CPU(int, x86_cpu_to_logical_apicid);
-- 
1.7.7.6

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