* [PATCH] bitmap: bitmap_equal memcmp optimization [not found] <1465288661-3273-1-git-send-email-schwidefsky@de.ibm.com> @ 2016-06-07 8:37 ` Martin Schwidefsky 2016-06-08 20:42 ` Andrew Morton 0 siblings, 1 reply; 3+ messages in thread From: Martin Schwidefsky @ 2016-06-07 8:37 UTC (permalink / raw) To: linux-arch, linux-kernel, Benjamin Herrenschmidt, David S. Miller Cc: Martin Schwidefsky The bitmap_equal function has optimized code for small bitmaps with less than BITS_PER_LONG bits. For larger bitmaps the out-of-line function __bitmap_equal is called. For a constant number of bits divisible by BITS_PER_LONG the memcmp function can be used. For s390 gcc knows how to optimize this function, memcmp calls with up to 256 bytes / 2048 bits are translated into a single instruction. Reviewed-by: David Hildenbrand <dahi@linux.vnet.ibm.com> Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com> --- include/linux/bitmap.h | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h index e9b0b9a..27bfc0b 100644 --- a/include/linux/bitmap.h +++ b/include/linux/bitmap.h @@ -267,6 +267,10 @@ static inline int bitmap_equal(const unsigned long *src1, { if (small_const_nbits(nbits)) return ! ((*src1 ^ *src2) & BITMAP_LAST_WORD_MASK(nbits)); +#ifdef CONFIG_S390 + else if (__builtin_constant_p(nbits) && (nbits % BITS_PER_LONG) == 0) + return !memcmp(src1, src2, nbits / 8); +#endif else return __bitmap_equal(src1, src2, nbits); } -- 2.6.6 ^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] bitmap: bitmap_equal memcmp optimization 2016-06-07 8:37 ` [PATCH] bitmap: bitmap_equal memcmp optimization Martin Schwidefsky @ 2016-06-08 20:42 ` Andrew Morton 2016-06-09 6:31 ` Martin Schwidefsky 0 siblings, 1 reply; 3+ messages in thread From: Andrew Morton @ 2016-06-08 20:42 UTC (permalink / raw) To: Martin Schwidefsky Cc: linux-arch, linux-kernel, Benjamin Herrenschmidt, David S. Miller On Tue, 7 Jun 2016 10:37:41 +0200 Martin Schwidefsky <schwidefsky@de.ibm.com> wrote: > The bitmap_equal function has optimized code for small bitmaps with less > than BITS_PER_LONG bits. For larger bitmaps the out-of-line function > __bitmap_equal is called. > > For a constant number of bits divisible by BITS_PER_LONG the memcmp > function can be used. For s390 gcc knows how to optimize this function, > memcmp calls with up to 256 bytes / 2048 bits are translated into a > single instruction. Patch looks simple enough, although it would benefit from a comment explaining what's special about s390. > --- a/include/linux/bitmap.h > +++ b/include/linux/bitmap.h > @@ -267,6 +267,10 @@ static inline int bitmap_equal(const unsigned long *src1, > { > if (small_const_nbits(nbits)) > return ! ((*src1 ^ *src2) & BITMAP_LAST_WORD_MASK(nbits)); > +#ifdef CONFIG_S390 > + else if (__builtin_constant_p(nbits) && (nbits % BITS_PER_LONG) == 0) > + return !memcmp(src1, src2, nbits / 8); > +#endif > else > return __bitmap_equal(src1, src2, nbits); > } Those elses are a bit daffy. This: --- a/include/linux/bitmap.h~bitmap-bitmap_equal-memcmp-optimization-fix +++ a/include/linux/bitmap.h @@ -266,13 +266,12 @@ static inline int bitmap_equal(const uns const unsigned long *src2, unsigned int nbits) { if (small_const_nbits(nbits)) - return ! ((*src1 ^ *src2) & BITMAP_LAST_WORD_MASK(nbits)); + return !((*src1 ^ *src2) & BITMAP_LAST_WORD_MASK(nbits)); #ifdef CONFIG_S390 - else if (__builtin_constant_p(nbits) && (nbits % BITS_PER_LONG) == 0) + if (__builtin_constant_p(nbits) && (nbits % BITS_PER_LONG) == 0) return !memcmp(src1, src2, nbits / 8); #endif - else - return __bitmap_equal(src1, src2, nbits); + return __bitmap_equal(src1, src2, nbits); } static inline int bitmap_intersects(const unsigned long *src1, _ ^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] bitmap: bitmap_equal memcmp optimization 2016-06-08 20:42 ` Andrew Morton @ 2016-06-09 6:31 ` Martin Schwidefsky 0 siblings, 0 replies; 3+ messages in thread From: Martin Schwidefsky @ 2016-06-09 6:31 UTC (permalink / raw) To: Andrew Morton Cc: linux-arch, linux-kernel, Benjamin Herrenschmidt, David S. Miller On Wed, 8 Jun 2016 13:42:12 -0700 Andrew Morton <akpm@linux-foundation.org> wrote: > On Tue, 7 Jun 2016 10:37:41 +0200 Martin Schwidefsky <schwidefsky@de.ibm.com> wrote: > > > The bitmap_equal function has optimized code for small bitmaps with less > > than BITS_PER_LONG bits. For larger bitmaps the out-of-line function > > __bitmap_equal is called. > > > > For a constant number of bits divisible by BITS_PER_LONG the memcmp > > function can be used. For s390 gcc knows how to optimize this function, > > memcmp calls with up to 256 bytes / 2048 bits are translated into a > > single instruction. > > Patch looks simple enough, although it would benefit from a comment > explaining what's special about s390. The explanation from the git commit could be transfered into a comment. > > --- a/include/linux/bitmap.h > > +++ b/include/linux/bitmap.h > > @@ -267,6 +267,10 @@ static inline int bitmap_equal(const unsigned long *src1, > > { > > if (small_const_nbits(nbits)) > > return ! ((*src1 ^ *src2) & BITMAP_LAST_WORD_MASK(nbits)); > > +#ifdef CONFIG_S390 > > + else if (__builtin_constant_p(nbits) && (nbits % BITS_PER_LONG) == 0) > > + return !memcmp(src1, src2, nbits / 8); > > +#endif > > else > > return __bitmap_equal(src1, src2, nbits); > > } > > Those elses are a bit daffy. This: > > --- a/include/linux/bitmap.h~bitmap-bitmap_equal-memcmp-optimization-fix > +++ a/include/linux/bitmap.h > @@ -266,13 +266,12 @@ static inline int bitmap_equal(const uns > const unsigned long *src2, unsigned int nbits) > { > if (small_const_nbits(nbits)) > - return ! ((*src1 ^ *src2) & BITMAP_LAST_WORD_MASK(nbits)); > + return !((*src1 ^ *src2) & BITMAP_LAST_WORD_MASK(nbits)); > #ifdef CONFIG_S390 > - else if (__builtin_constant_p(nbits) && (nbits % BITS_PER_LONG) == 0) > + if (__builtin_constant_p(nbits) && (nbits % BITS_PER_LONG) == 0) > return !memcmp(src1, src2, nbits / 8); > #endif > - else > - return __bitmap_equal(src1, src2, nbits); > + return __bitmap_equal(src1, src2, nbits); > } > > static inline int bitmap_intersects(const unsigned long *src1, > _ > Yeah that looks better. Thanks for picking this up! -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. ^ permalink raw reply [flat|nested] 3+ messages in thread
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2016-06-07 8:37 ` [PATCH] bitmap: bitmap_equal memcmp optimization Martin Schwidefsky
2016-06-08 20:42 ` Andrew Morton
2016-06-09 6:31 ` Martin Schwidefsky
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