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Subject[PATCH] x86: page: get_order() optimization
Date
For x86 architecture get_order function can be optimized due to
assembler instruction bsr.
---
arch/x86/include/asm/page.h | 20 +++++++++++++++++++-
1 files changed, 19 insertions(+), 1 deletions(-)

diff --git a/arch/x86/include/asm/page.h b/arch/x86/include/asm/page.h
index 8ca8283..339ae26 100644
--- a/arch/x86/include/asm/page.h
+++ b/arch/x86/include/asm/page.h
@@ -60,10 +60,28 @@ static inline void copy_user_page(void *to, void *from, unsigned long vaddr,
extern bool __virt_addr_valid(unsigned long kaddr);
#define virt_addr_valid(kaddr) __virt_addr_valid((unsigned long) (kaddr))

+/* Pure 2^n version of get_order */
+static inline __attribute_const__ int get_order(unsigned long size)
+{
+ int order;
+
+ size = (size - 1) >> (PAGE_SHIFT - 1);
+#ifdef CONFIG_X86_CMOV
+ asm("bsr %1,%0\n\t"
+ "cmovzl %2,%0"
+ : "=&r" (order) : "rm" (size), "rm" (0));
+#else
+ asm("bsr %1,%0\n\t"
+ "jnz 1f\n\t"
+ "movl $0,%0\n"
+ "1:" : "=r" (order) : "rm" (size));
+#endif
+ return order;
+}
+
#endif /* __ASSEMBLY__ */

#include <asm-generic/memory_model.h>
-#include <asm-generic/getorder.h>

#define __HAVE_ARCH_GATE_AREA 1

--
1.7.2.3


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