From 0816b0f0365539c8f6280634d2c1778d0108d8f5 Mon Sep 17 00:00:00 2001 From: Vlad Zolotarov Date: Mon, 11 Jun 2012 12:56:52 +0300 Subject: 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 Acked-by: Shai Fultheim Cc: Shai Fultheim (Shai@ScaleMP.com) Cc: ido@wizery.com Cc: Linus Torvalds Cc: Andrew Morton Cc: Peter Zijlstra Link: http://lkml.kernel.org/r/1719258.EYKzE4Zbq5@vlad Signed-off-by: Ingo Molnar --- arch/x86/kernel/setup_percpu.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) (limited to 'arch/x86/kernel/setup_percpu.c') 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 #include -DEFINE_PER_CPU(int, cpu_number); +DEFINE_PER_CPU_READ_MOSTLY(int, cpu_number); EXPORT_PER_CPU_SYMBOL(cpu_number); #ifdef CONFIG_X86_64 -- cgit v1.2.3