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authorVlad Zolotarov <vlad@scalemp.com>2012-06-11 12:56:52 +0300
committerIngo Molnar <mingo@kernel.org>2012-06-14 12:42:11 +0200
commit0816b0f0365539c8f6280634d2c1778d0108d8f5 (patch)
tree92ee18c8ca0475e636558a36572f28d62bcc627d /arch/x86/kernel/setup_percpu.c
parentc35f77417ebfc7c21c02aa9c8c30aa4cecf331d6 (diff)
download96b-common-0816b0f0365539c8f6280634d2c1778d0108d8f5.tar.gz
x86: Add read_mostly declaration/definition to variables from smp.h
Add "read-mostly" qualifier to the following variables in smp.h: - cpu_sibling_map - cpu_core_map - cpu_llc_shared_map - cpu_llc_id - cpu_number - x86_cpu_to_apicid - x86_bios_cpu_apicid - x86_cpu_to_logical_apicid As long as all the variables above are only written during the initialization, this change is meant to prevent the false sharing. More specifically, on vSMP Foundation platform x86_cpu_to_apicid shared the same internode_cache_line with frequently written lapic_events. From the analysis of the first 33 per_cpu variables out of 219 (memories they describe, to be more specific) the 8 have read_mostly nature (tlb_vector_offset, cpu_loops_per_jiffy, xen_debug_irq, etc.) and 25 are frequently written (irq_stack_union, gdt_page, exception_stacks, idt_desc, etc.). Assuming that the spread of the rest of the per_cpu variables is similar, identifying the read mostly memories will make more sense in terms of long-term code maintenance comparing to identifying frequently written memories. Signed-off-by: Vlad Zolotarov <vlad@scalemp.com> Acked-by: Shai Fultheim <shai@scalemp.com> Cc: Shai Fultheim (Shai@ScaleMP.com) <Shai@scalemp.com> Cc: ido@wizery.com Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Peter Zijlstra <a.p.zijlstra@chello.nl> Link: http://lkml.kernel.org/r/1719258.EYKzE4Zbq5@vlad Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'arch/x86/kernel/setup_percpu.c')
-rw-r--r--arch/x86/kernel/setup_percpu.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/arch/x86/kernel/setup_percpu.c b/arch/x86/kernel/setup_percpu.c
index 5a98aa272184..5cdff0357746 100644
--- a/arch/x86/kernel/setup_percpu.c
+++ b/arch/x86/kernel/setup_percpu.c
@@ -21,7 +21,7 @@
#include <asm/cpu.h>
#include <asm/stackprotector.h>
-DEFINE_PER_CPU(int, cpu_number);
+DEFINE_PER_CPU_READ_MOSTLY(int, cpu_number);
EXPORT_PER_CPU_SYMBOL(cpu_number);
#ifdef CONFIG_X86_64