xiaomi-sm8450/android_kernel_xiaomi_sm8450
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

x86: Add read_mostly declaration/definition to variables from smp.h

Browse Source 
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>
This commit is contained in:
Vlad Zolotarov
2012-06-11 12:56:52 +03:00
committed by Ingo Molnar
parent c35f77417e
commit 0816b0f036
5 changed files with 17 additions and 17 deletions
Download Patch File Download Diff File Expand all files Collapse all files

16
arch/x86/include/asm/smp.h
View File

@@ -31,12 +31,12 @@ static inline bool cpu_has_ht_siblings(void)
return has_siblings;
}
DECLARE_PER_CPU(cpumask_var_t, cpu_sibling_map);
DECLARE_PER_CPU(cpumask_var_t, cpu_core_map);
DECLARE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_sibling_map);
DECLARE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_core_map);
/* cpus sharing the last level cache: */
DECLARE_PER_CPU(cpumask_var_t, cpu_llc_shared_map);
DECLARE_PER_CPU(u16, cpu_llc_id);
DECLARE_PER_CPU(int, cpu_number);
DECLARE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_llc_shared_map);
DECLARE_PER_CPU_READ_MOSTLY(u16, cpu_llc_id);
DECLARE_PER_CPU_READ_MOSTLY(int, cpu_number);
static inline struct cpumask *cpu_sibling_mask(int cpu)
{
@@ -53,10 +53,10 @@ 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(u16, x86_bios_cpu_apicid);
DECLARE_EARLY_PER_CPU_READ_MOSTLY(u16, x86_cpu_to_apicid);
DECLARE_EARLY_PER_CPU_READ_MOSTLY(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);
DECLARE_EARLY_PER_CPU_READ_MOSTLY(int, x86_cpu_to_logical_apicid);
#endif
/* Static state in head.S used to set up a CPU */