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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>
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
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
arch/x86/include/asm/apic.h
View File

@ -537,7 +537,7 @@ static inline const struct cpumask *default_target_cpus(void)
#endif #endif
} }
DECLARE_EARLY_PER_CPU(u16, x86_bios_cpu_apicid); DECLARE_EARLY_PER_CPU_READ_MOSTLY(u16, x86_bios_cpu_apicid);
static inline unsigned int read_apic_id(void) static inline unsigned int read_apic_id(void)

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

@ -31,12 +31,12 @@ static inline bool cpu_has_ht_siblings(void)
return has_siblings; return has_siblings;
} }
DECLARE_PER_CPU(cpumask_var_t, cpu_sibling_map); DECLARE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_sibling_map);
DECLARE_PER_CPU(cpumask_var_t, cpu_core_map); DECLARE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_core_map);
/* cpus sharing the last level cache: */ /* cpus sharing the last level cache: */
DECLARE_PER_CPU(cpumask_var_t, cpu_llc_shared_map); DECLARE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_llc_shared_map);
DECLARE_PER_CPU(u16, cpu_llc_id); DECLARE_PER_CPU_READ_MOSTLY(u16, cpu_llc_id);
DECLARE_PER_CPU(int, cpu_number); DECLARE_PER_CPU_READ_MOSTLY(int, cpu_number);
static inline struct cpumask *cpu_sibling_mask(int cpu) 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); 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); DECLARE_EARLY_PER_CPU_READ_MOSTLY(u16, x86_bios_cpu_apicid);
#if defined(CONFIG_X86_LOCAL_APIC) && defined(CONFIG_X86_32) #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 #endif
/* Static state in head.S used to set up a CPU */ /* Static state in head.S used to set up a CPU */

6
arch/x86/kernel/apic/apic.c
View File

@ -75,8 +75,8 @@ physid_mask_t phys_cpu_present_map;
/* /*
* Map cpu index to physical APIC ID * Map cpu index to physical APIC ID
*/ */
DEFINE_EARLY_PER_CPU(u16, x86_cpu_to_apicid, BAD_APICID); DEFINE_EARLY_PER_CPU_READ_MOSTLY(u16, x86_cpu_to_apicid, BAD_APICID);
DEFINE_EARLY_PER_CPU(u16, x86_bios_cpu_apicid, BAD_APICID); DEFINE_EARLY_PER_CPU_READ_MOSTLY(u16, x86_bios_cpu_apicid, BAD_APICID);
EXPORT_EARLY_PER_CPU_SYMBOL(x86_cpu_to_apicid); EXPORT_EARLY_PER_CPU_SYMBOL(x86_cpu_to_apicid);
EXPORT_EARLY_PER_CPU_SYMBOL(x86_bios_cpu_apicid); EXPORT_EARLY_PER_CPU_SYMBOL(x86_bios_cpu_apicid);
@ -88,7 +88,7 @@ EXPORT_EARLY_PER_CPU_SYMBOL(x86_bios_cpu_apicid);
* used for the mapping. This is where the behaviors of x86_64 and 32 * used for the mapping. This is where the behaviors of x86_64 and 32
* actually diverge. Let's keep it ugly for now. * actually diverge. Let's keep it ugly for now.
*/ */
DEFINE_EARLY_PER_CPU(int, x86_cpu_to_logical_apicid, BAD_APICID); DEFINE_EARLY_PER_CPU_READ_MOSTLY(int, x86_cpu_to_logical_apicid, BAD_APICID);
/* /*
* Knob to control our willingness to enable the local APIC. * Knob to control our willingness to enable the local APIC.

2
arch/x86/kernel/setup_percpu.c
View File

@ -21,7 +21,7 @@
#include <asm/cpu.h> #include <asm/cpu.h>
#include <asm/stackprotector.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); EXPORT_PER_CPU_SYMBOL(cpu_number);
#ifdef CONFIG_X86_64 #ifdef CONFIG_X86_64

8
arch/x86/kernel/smpboot.c
View File

@ -104,17 +104,17 @@ int smp_num_siblings = 1;
EXPORT_SYMBOL(smp_num_siblings); EXPORT_SYMBOL(smp_num_siblings);
/* Last level cache ID of each logical CPU */ /* Last level cache ID of each logical CPU */
DEFINE_PER_CPU(u16, cpu_llc_id) = BAD_APICID; DEFINE_PER_CPU_READ_MOSTLY(u16, cpu_llc_id) = BAD_APICID;
/* representing HT siblings of each logical CPU */ /* representing HT siblings of each logical CPU */
DEFINE_PER_CPU(cpumask_var_t, cpu_sibling_map); DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_sibling_map);
EXPORT_PER_CPU_SYMBOL(cpu_sibling_map); EXPORT_PER_CPU_SYMBOL(cpu_sibling_map);
/* representing HT and core siblings of each logical CPU */ /* representing HT and core siblings of each logical CPU */
DEFINE_PER_CPU(cpumask_var_t, cpu_core_map); DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_core_map);
EXPORT_PER_CPU_SYMBOL(cpu_core_map); EXPORT_PER_CPU_SYMBOL(cpu_core_map);
DEFINE_PER_CPU(cpumask_var_t, cpu_llc_shared_map); DEFINE_PER_CPU_READ_MOSTLY(cpumask_var_t, cpu_llc_shared_map);
/* Per CPU bogomips and other parameters */ /* Per CPU bogomips and other parameters */
DEFINE_PER_CPU_SHARED_ALIGNED(struct cpuinfo_x86, cpu_info); DEFINE_PER_CPU_SHARED_ALIGNED(struct cpuinfo_x86, cpu_info);