[PATCH v5 2/2] x86: Added read_mostly declaration/definition to vars from smp.h

[Vlad Zolotarov]

Added "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@xxxxxxxxxxx>
Acked-by: Shai Fultheim <shai@xxxxxxxxxxx>
---
 arch/x86/include/asm/apic.h    |    2 +-
 arch/x86/include/asm/smp.h     |   16 ++++++++--------
 arch/x86/kernel/apic/apic.c    |    6 +++---
 arch/x86/kernel/setup_percpu.c |    2 +-
 arch/x86/kernel/smpboot.c      |    8 ++++----
 5 files changed, 17 insertions(+), 17 deletions(-)

diff --git a/arch/x86/include/asm/apic.h b/arch/x86/include/asm/apic.h
index d854101..ca11940 100644
--- a/arch/x86/include/asm/apic.h
+++ b/arch/x86/include/asm/apic.h
@@ -520,7 +520,7 @@ static inline const struct cpumask *default_target_cpus(void)
 #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)
diff --git a/arch/x86/include/asm/smp.h b/arch/x86/include/asm/smp.h
index 0434c40..2a5304a 100644
--- a/arch/x86/include/asm/smp.h
+++ b/arch/x86/include/asm/smp.h
@@ -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 */
diff --git a/arch/x86/kernel/apic/apic.c b/arch/x86/kernel/apic/apic.c
index edc2448..33c3672 100644
--- a/arch/x86/kernel/apic/apic.c
+++ b/arch/x86/kernel/apic/apic.c
@@ -74,8 +74,8 @@ physid_mask_t phys_cpu_present_map;
 /*
  * Map cpu index to physical APIC ID
  */
-DEFINE_EARLY_PER_CPU(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_cpu_to_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_bios_cpu_apicid);
 
@@ -87,7 +87,7 @@ EXPORT_EARLY_PER_CPU_SYMBOL(x86_bios_cpu_apicid);
  * used for the mapping.  This is where the behaviors of x86_64 and 32
  * 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.
diff --git a/arch/x86/kernel/setup_percpu.c b/arch/x86/kernel/setup_percpu.c
index 5a98aa2..5cdff03 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
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 6e1e406..3d877b1 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -118,17 +118,17 @@ int smp_num_siblings = 1;
 EXPORT_SYMBOL(smp_num_siblings);
 
 /* 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 */
-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);
 
 /* 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);
 
-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 */
 DEFINE_PER_CPU_SHARED_ALIGNED(struct cpuinfo_x86, cpu_info);
-- 
1.7.5.4


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