linux-kernel - [PATCH] Bitmap: Optimized division operation to shift operation

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Message-Id: <1586935667-4792-1-git-send-email-wangqing@vivo.com>
Date:   Wed, 15 Apr 2020 15:27:40 +0800
From:   Wang Qing <wangqing@...o.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Dennis Zhou <dennis@...nel.org>,
        Wolfram Sang <wsa+renesas@...g-engineering.com>,
        David Sterba <dsterba@...e.com>,
        Josef Bacik <josef@...icpanda.com>,
        Stefano Brivio <sbrivio@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        William Breathitt Gray <vilhelm.gray@...il.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Yury Norov <yury.norov@...il.com>,
        Wang Qing <wangqing@...o.com>, linux-kernel@...r.kernel.org
Cc:     opensource.kernel@...o.com
Subject: [PATCH] Bitmap: Optimized division operation to shift operation

On some processors, the / operate will call the compiler`s div lib,
which is low efficient. Bitmap is performance sensitive, We can
replace the / operation with shift.

Signed-off-by: Wang Qing <wangqing@...o.com>
---
 include/linux/bitmap.h | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 99058eb..85ff982 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -337,7 +337,7 @@ static inline int bitmap_equal(const unsigned long *src1,
 		return !((*src1 ^ *src2) & BITMAP_LAST_WORD_MASK(nbits));
 	if (__builtin_constant_p(nbits & BITMAP_MEM_MASK) &&
 	    IS_ALIGNED(nbits, BITMAP_MEM_ALIGNMENT))
-		return !memcmp(src1, src2, nbits / 8);
+		return !memcmp(src1, src2, nbits >> 3);
 	return __bitmap_equal(src1, src2, nbits);
 }
 
@@ -411,7 +411,7 @@ static __always_inline void bitmap_set(unsigned long *map, unsigned int start,
 		 IS_ALIGNED(start, BITMAP_MEM_ALIGNMENT) &&
 		 __builtin_constant_p(nbits & BITMAP_MEM_MASK) &&
 		 IS_ALIGNED(nbits, BITMAP_MEM_ALIGNMENT))
-		memset((char *)map + start / 8, 0xff, nbits / 8);
+		memset((char *)map + (start >> 3), 0xff, nbits >> 3);
 	else
 		__bitmap_set(map, start, nbits);
 }
@@ -425,7 +425,7 @@ static __always_inline void bitmap_clear(unsigned long *map, unsigned int start,
 		 IS_ALIGNED(start, BITMAP_MEM_ALIGNMENT) &&
 		 __builtin_constant_p(nbits & BITMAP_MEM_MASK) &&
 		 IS_ALIGNED(nbits, BITMAP_MEM_ALIGNMENT))
-		memset((char *)map + start / 8, 0, nbits / 8);
+		memset((char *)map + (start >> 3), 0, nbits >> 3);
 	else
 		__bitmap_clear(map, start, nbits);
 }
-- 
2.7.4