Search Linux Wireless

[PATCH v8 01/15] x86/common: Align cpu_caps_cleared and cpu_caps_set to unsigned long

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



cpu_caps_cleared[] and cpu_caps_set[] may not be aligned to unsigned long.
Atomic operations (i.e. set_bit() and clear_bit()) on the bitmaps may
access two cache lines (a.k.a. split lock) and cause the CPU to do a bus
lock to block all memory accesses from other processors to ensure
atomicity.

To avoid the overall performance degradation from the bus locking, align
the two variables to unsigned long.

Defining the variables as unsigned long may also fix the issue because
they will be naturally aligned to unsigned long. But that needs additional
code changes. Adding __aligned(unsigned long) is a simpler fix.

Signed-off-by: Fenghua Yu <fenghua.yu@xxxxxxxxx>
Reviewed-by: Borislav Petkov <bp@xxxxxxx>
---
 arch/x86/kernel/cpu/common.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kernel/cpu/common.c b/arch/x86/kernel/cpu/common.c
index cb28e98a0659..3716e2bb028b 100644
--- a/arch/x86/kernel/cpu/common.c
+++ b/arch/x86/kernel/cpu/common.c
@@ -488,8 +488,9 @@ static const char *table_lookup_model(struct cpuinfo_x86 *c)
 	return NULL;		/* Not found */
 }
 
-__u32 cpu_caps_cleared[NCAPINTS + NBUGINTS];
-__u32 cpu_caps_set[NCAPINTS + NBUGINTS];
+/* Aligned to unsigned long to avoid split lock in atomic bitmap ops */
+__u32 cpu_caps_cleared[NCAPINTS + NBUGINTS] __aligned(sizeof(unsigned long));
+__u32 cpu_caps_set[NCAPINTS + NBUGINTS] __aligned(sizeof(unsigned long));
 
 void load_percpu_segment(int cpu)
 {
-- 
2.19.1




[Index of Archives]     [Linux Host AP]     [ATH6KL]     [Linux Wireless Personal Area Network]     [Linux Bluetooth]     [Wireless Regulations]     [Linux Netdev]     [Kernel Newbies]     [Linux Kernel]     [IDE]     [Git]     [Netfilter]     [Bugtraq]     [Yosemite Hiking]     [MIPS Linux]     [ARM Linux]     [Linux RAID]

  Powered by Linux