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Date: Fri, 1 Apr 2011 22:18:13 +0300
From: Maksym Planeta <mcsim.planeta@...il.com>
To: mingo@...hat.com
Cc: kernel-janitors@...r.kernel.org, linux-kernel@...r.kernel.org,
hpa@...or.com, Maksym Planeta <mcsim.planeta@...il.com>
Subject: [PATCH] page: get_order() optimization
Loop was repalaced with __builtin_clz(). This still allows to precompute
constants, but on some architectures it uses special instruction to
calculate order.
Signed-off-by: Maksym Planeta <mcsim.planeta@...il.com>
---
include/asm-generic/getorder.h | 8 +++-----
1 files changed, 3 insertions(+), 5 deletions(-)
diff --git a/include/asm-generic/getorder.h b/include/asm-generic/getorder.h
index 67e7245..fe8020c 100644
--- a/include/asm-generic/getorder.h
+++ b/include/asm-generic/getorder.h
@@ -11,11 +11,9 @@ static inline __attribute_const__ int get_order(unsigned long size)
int order;
size = (size - 1) >> (PAGE_SHIFT - 1);
- order = -1;
- do {
- size >>= 1;
- order++;
- } while (size);
+ order = (__builtin_clzl(size) ^ (BITS_PER_LONG - 1));
+ if (size == 0)
+ order = 0;
return order;
}
--
1.7.2.3
--
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