For x86 architecture get_order function can be optimized due to
assembler instruction bsr.
This is second version of patch where for constants gcc precompute the
result.
Signed-off-by: Maksym Planeta <mcsim.planeta@xxxxxxxxx>
---
arch/x86/include/asm/getorder.h | 48 +++++++++++++++++++++++++++++++++++++++
arch/x86/include/asm/page.h | 2 +-
2 files changed, 49 insertions(+), 1 deletions(-)
create mode 100644 arch/x86/include/asm/getorder.h
diff --git a/arch/x86/include/asm/getorder.h b/arch/x86/include/asm/getorder.h
new file mode 100644
index 0000000..b0c6f57
--- /dev/null
+++ b/arch/x86/include/asm/getorder.h
@@ -0,0 +1,48 @@
+#ifndef __ASM_GENERIC_GETORDER_H
+#define __ASM_GENERIC_GETORDER_H
+
+#ifndef __ASSEMBLY__
+
+#include <linux/compiler.h>
+
+#ifdef CONFIG_X86_CMOV
+#define ASM_CMOVZ(op, dest) \
+ "cmovzl %" #op ",%" #dest ";\n\t"
+#else
+#define ASM_CMOVZ(op, dest) \
+ "jnz 1f;\n\t" \
+ "movl %" #op ", %" #dest ";\n\t" \
+ "1: "
+#endif
+
+static __always_inline int __get_order(unsigned long size)
+{
+ int order;
+
+ size = (size - 1) >> (PAGE_SHIFT - 1);
+ asm("bsr %1, %0\n\t"
+ ASM_CMOVZ(2, 0)
+ : "=&r" (order) : "rm" (size), "rm" (0));
+ return order;
+}
+
+/* Pure 2^n version of get_order */
+static inline __attribute_const__ int get_order(unsigned long size)
+{
+ int order;
+
+ if (__builtin_constant_p(size)) {
+ size = (size - 1) >> (PAGE_SHIFT - 1);
+ order = -1;
+ do {
+ size >>= 1;
+ order++;
+ } while (size);
+ return order;
+ }
+ return __get_order(size);
+}
+
+#endif /* __ASSEMBLY__ */
+
+#endif /* __ASM_GENERIC_GETORDER_H */
diff --git a/arch/x86/include/asm/page.h b/arch/x86/include/asm/page.h
index 8ca8283..10e4c45 100644
--- a/arch/x86/include/asm/page.h
+++ b/arch/x86/include/asm/page.h
@@ -63,7 +63,7 @@ extern bool __virt_addr_valid(unsigned long kaddr);
#endif /* __ASSEMBLY__ */
#include <asm-generic/memory_model.h>
-#include <asm-generic/getorder.h>
+#include <asm/getorder.h>
#define __HAVE_ARCH_GATE_AREA 1
--
1.7.2.3
--
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