On Wed, Jan 20, 2021 at 04:06:29PM -0800, Yury Norov wrote:
Similarly to bitmap functions, find_next_*_bit() users will benefit
if we'll handle a case of bitmaps that fit into a single word. In the
very best case, the compiler may replace a function call with a
single ffs or ffz instruction.
+ if (small_const_nbits(size)) {
+ unsigned long val;
+
+ if (unlikely(offset >= size))
+ return size;
+ val = *addr & BITMAP_FIRST_WORD_MASK(offset)
+ & BITMAP_LAST_WORD_MASK(size);
Seems like a new helper can be introduced (BITS or BITMAP namespace depending
on the decision):
#define _OFFSET_SIZE_MASK(o,s) \
(BITMAP_FIRST_WORD_MASK(o) & BITMAP_LAST_WORD_MASK(s))
val = *addr & BITMAP_OFFSET_SIZE_MASK(offset, size);
And so on below.
+ return val ? __ffs(val) : size;
+ }
--
With Best Regards,
Andy Shevchenko
