Messages in this thread | | | Date | Thu, 17 Aug 2023 12:37:04 +0300 | From | Andy Shevchenko <> | Subject | Re: [PATCH] bitmap: optimize bitmap_remap() |
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On Tue, Aug 15, 2023 at 04:59:34PM -0700, Yury Norov wrote: > When 'new' map is empty, i.e. identity mapping, we can simply copy > src to dst, which is significantly faster than setting bits one by > one in a for-loop.
> While here, replace set_bit() with non-atomic __set_bit().
I believe this requires a separate change with additional words why it's okay to drop atomicity.
...
> for_each_set_bit(oldbit, src, nbits) { > int n = bitmap_pos_to_ord(old, oldbit, nbits); > > + bit = (n < 0) ? oldbit : /* identity map */
Can't you also optimize this case?
Something like
bitmap_xor(tmp, old, new) // maybe even better approach, dunno bitmap_empty(tmp) // can be replaced by find first bit
?
> + find_nth_bit(new, nbits, n % w); > + __set_bit(bit, dst); > }
-- With Best Regards, Andy Shevchenko
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