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Date: Thu, 12 Nov 2015 08:43:04 +0800 From: Fan Li <fanofcode.li@...sung.com> To: 'Jaegeuk Kim' <jaegeuk@...nel.org> Cc: linux-kernel@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net Subject: [f2fs-dev] [PATCH] f2fs: optimize __find_rev_next_bit 1. Skip __reverse_ulong if the bitmap is empty. 2. Reduce branches and codes. According to my test, the performance of this new version is 5% higher on an empty bitmap of 64bytes, and remains about the same in the worst scenario. Signed-off-by: Fan li <fanofcode.li@...sung.com> --- fs/f2fs/segment.c | 46 ++++++++++++++++++---------------------------- 1 file changed, 18 insertions(+), 28 deletions(-) diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c index f77b325..efbf6b5 100644 --- a/fs/f2fs/segment.c +++ b/fs/f2fs/segment.c @@ -86,6 +86,7 @@ static inline unsigned long __reverse_ffs(unsigned long word) /* * __find_rev_next(_zero)_bit is copied from lib/find_next_bit.c because * f2fs_set_bit makes MSB and LSB reversed in a byte. + * @size must be integral times of unsigned long. * Example: * MSB <--> LSB * f2fs_set_bit(0, bitmap) => 1000 0000 @@ -95,47 +96,36 @@ static unsigned long __find_rev_next_bit(const unsigned long *addr, unsigned long size, unsigned long offset) { const unsigned long *p = addr + BIT_WORD(offset); - unsigned long result = offset & ~(BITS_PER_LONG - 1); + unsigned long result = size; unsigned long tmp; if (offset >= size) return size; - size -= result; + size -= (offset & ~(BITS_PER_LONG - 1)); offset %= BITS_PER_LONG; - if (!offset) - goto aligned; - tmp = __reverse_ulong((unsigned char *)p); - tmp &= ~0UL >> offset; - - if (size < BITS_PER_LONG) - goto found_first; - if (tmp) - goto found_middle; + while (1) { + if (*p == 0) + goto pass; - size -= BITS_PER_LONG; - result += BITS_PER_LONG; - p++; -aligned: - while (size & ~(BITS_PER_LONG-1)) { tmp = __reverse_ulong((unsigned char *)p); + + tmp &= ~0UL >> offset; + if (size < BITS_PER_LONG) + tmp &= (~0UL << (BITS_PER_LONG - size)); if (tmp) - goto found_middle; - result += BITS_PER_LONG; + goto found; +pass: + if (size <= BITS_PER_LONG) + break; size -= BITS_PER_LONG; + offset = 0; p++; } - if (!size) - return result; - - tmp = __reverse_ulong((unsigned char *)p); -found_first: - tmp &= (~0UL << (BITS_PER_LONG - size)); - if (!tmp) /* Are any bits set? */ - return result + size; /* Nope. */ -found_middle: - return result + __reverse_ffs(tmp); + return result; +found: + return result - size + __reverse_ffs(tmp); } static unsigned long __find_rev_next_zero_bit(const unsigned long *addr, -- 1.7.9.5 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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