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Subject[thisops uV3 07/18] highmem: Use this_cpu_xx_return() operations
Use this_cpu operations to optimize access primitives for highmem.

The main effect is the avoidance of address calculations through the
use of a segment prefix.

Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Christoph Lameter <cl@linux.com>

---
include/linux/highmem.h | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
Index: linux-2.6/include/linux/highmem.h
===================================================================
--- linux-2.6.orig/include/linux/highmem.h 2010-11-22 14:43:40.000000000 -0600
+++ linux-2.6/include/linux/highmem.h 2010-11-22 14:45:02.000000000 -0600
@@ -81,7 +81,8 @@ DECLARE_PER_CPU(int, __kmap_atomic_idx);

static inline int kmap_atomic_idx_push(void)
{
- int idx = __get_cpu_var(__kmap_atomic_idx)++;
+ int idx = __this_cpu_inc_return(__kmap_atomic_idx) - 1;
+
#ifdef CONFIG_DEBUG_HIGHMEM
WARN_ON_ONCE(in_irq() && !irqs_disabled());
BUG_ON(idx > KM_TYPE_NR);
@@ -91,12 +92,12 @@ static inline int kmap_atomic_idx_push(v

static inline int kmap_atomic_idx(void)
{
- return __get_cpu_var(__kmap_atomic_idx) - 1;
+ return __this_cpu_read(__kmap_atomic_idx) - 1;
}

static inline int kmap_atomic_idx_pop(void)
{
- int idx = --__get_cpu_var(__kmap_atomic_idx);
+ int idx = __this_cpu_dec_return(__kmap_atomic_idx);
#ifdef CONFIG_DEBUG_HIGHMEM
BUG_ON(idx < 0);
#endif


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