* [PATCH] Bitmap: Optimized division operation to shift operation
@ 2020-04-15 7:27 Wang Qing
2020-04-15 7:47 ` Joe Perches
2020-04-15 8:56 ` Peter Zijlstra
0 siblings, 2 replies; 3+ messages in thread
From: Wang Qing @ 2020-04-15 7:27 UTC (permalink / raw)
To: Andrew Morton, Dennis Zhou, Wolfram Sang, David Sterba,
Josef Bacik, Stefano Brivio, Thomas Gleixner,
William Breathitt Gray, Randy Dunlap, Andy Shevchenko,
Yury Norov, Wang Qing, linux-kernel
Cc: opensource.kernel
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@vivo.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
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] Bitmap: Optimized division operation to shift operation
2020-04-15 7:27 [PATCH] Bitmap: Optimized division operation to shift operation Wang Qing
@ 2020-04-15 7:47 ` Joe Perches
2020-04-15 8:56 ` Peter Zijlstra
1 sibling, 0 replies; 3+ messages in thread
From: Joe Perches @ 2020-04-15 7:47 UTC (permalink / raw)
To: Wang Qing, Andrew Morton, Dennis Zhou, Wolfram Sang,
David Sterba, Josef Bacik, Stefano Brivio, Thomas Gleixner,
William Breathitt Gray, Randy Dunlap, Andy Shevchenko,
Yury Norov, linux-kernel
Cc: opensource.kernel
On Wed, 2020-04-15 at 15:27 +0800, Wang Qing wrote:
> 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.
Seems more like bad compilers than useful code changes
unless you can specify what compilers and what processors.
> diff --git 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);
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] Bitmap: Optimized division operation to shift operation
2020-04-15 7:27 [PATCH] Bitmap: Optimized division operation to shift operation Wang Qing
2020-04-15 7:47 ` Joe Perches
@ 2020-04-15 8:56 ` Peter Zijlstra
1 sibling, 0 replies; 3+ messages in thread
From: Peter Zijlstra @ 2020-04-15 8:56 UTC (permalink / raw)
To: Wang Qing
Cc: Andrew Morton, Dennis Zhou, Wolfram Sang, David Sterba,
Josef Bacik, Stefano Brivio, Thomas Gleixner,
William Breathitt Gray, Randy Dunlap, Andy Shevchenko,
Yury Norov, linux-kernel, opensource.kernel
On Wed, Apr 15, 2020 at 03:27:40PM +0800, Wang Qing wrote:
> 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@vivo.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);
> }
If your compiler gets this wrong, set it on fire and scatter its remains.
^ permalink raw reply [flat|nested] 3+ messages in thread
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2020-04-15 7:27 [PATCH] Bitmap: Optimized division operation to shift operation Wang Qing
2020-04-15 7:47 ` Joe Perches
2020-04-15 8:56 ` Peter Zijlstra
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