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Date: Fri, 24 Apr 2020 16:10:37 +0200 From: Lukas Wunner <lukas@...ner.de> To: Syed Nayyar Waris <syednwaris@...il.com> Cc: akpm@...ux-foundation.org, andriy.shevchenko@...ux.intel.com, vilhelm.gray@...il.com, arnd@...db.de, linus.walleij@...aro.org, linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH 1/6] bitops: Introduce the the for_each_set_clump macro On Fri, Apr 24, 2020 at 05:55:21PM +0530, Syed Nayyar Waris wrote: > +static inline void bitmap_set_value(unsigned long *map, > + unsigned long value, > + unsigned long start, unsigned long nbits) > +{ > + const size_t index = BIT_WORD(start); > + const unsigned long offset = start % BITS_PER_LONG; > + const unsigned long ceiling = roundup(start + 1, BITS_PER_LONG); > + const unsigned long space = ceiling - start; > + > + value &= GENMASK(nbits - 1, 0); > + > + if (space >= nbits) { > + map[index] &= ~(GENMASK(nbits + offset - 1, offset)); > + map[index] |= value << offset; > + } else { > + map[index] &= ~BITMAP_FIRST_WORD_MASK(start); > + map[index] |= value << offset; > + map[index + 1] &= ~BITMAP_LAST_WORD_MASK(start + nbits); > + map[index + 1] |= (value >> space); > + } > +} Sorry but what's the advantage of using this complicated function as a replacement for the much simpler bitmap_set_value8()? The drivers calling bitmap_set_value8() *know* that 8-bit accesses are possible and take advantage of that knowledge by using a small, speed-optimized function. Replacing that with a more complicated (potentially less performant) function doesn't seem to be a step forward. Thanks, Lukas
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