From: Maksym Planeta <mcsim.planeta@gmail.com>
To: mingo@redhat.com
Cc: kernel-janitors@vger.kernel.org, linux-kernel@vger.kernel.org,
hpa@zytor.com, Maksym Planeta <mcsim.planeta@gmail.com>
Subject: [PATCH] page: get_order() optimization
Date: Fri, 01 Apr 2011 19:18:13 +0000 [thread overview]
Message-ID: <1301685493-2567-1-git-send-email-mcsim.planeta@gmail.com> (raw)
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@gmail.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
next reply other threads:[~2011-04-01 19:18 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-04-01 19:18 Maksym Planeta [this message]
2011-04-01 19:34 ` [PATCH] page: get_order() optimization H. Peter Anvin
2011-04-02 13:06 ` Johannes Weiner
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