Messages in this thread | | | Date | Wed, 7 Sep 2022 09:57:30 -0700 | From | Yury Norov <> | Subject | Re: [PATCH v3 3/4] lib/find_bit: optimize find_next_bit() functions |
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On Wed, Sep 07, 2022 at 05:27:08PM +0100, Valentin Schneider wrote: > On 27/08/22 10:58, Yury Norov wrote: > > +#define FIND_NEXT_BIT(FETCH, MUNGE, size, start) \ > > +({ \ > > + unsigned long mask, idx, tmp, sz = (size), __start = (start); \ > > + \ > > + if (unlikely(__start >= sz)) \ > > + goto out; \ > > + \ > > + mask = MUNGE(BITMAP_FIRST_WORD_MASK(__start)); \ > > + idx = __start / BITS_PER_LONG; \ > > + \ > > + for (tmp = (FETCH) & mask; !tmp; tmp = (FETCH)) { \ > > + if (idx > sz / BITS_PER_LONG) \ > > Does that want to be
Yes, I already fixed this.
> if (idx + 1 >= sz / BITS_PER_LONG) > > ? > > Consider this as used in _find_next_bit() for an all-zero 128-bit wide > bitmap (two ULL's), providing the memory contiguous to the bitmap is also > zero then this will only stop at idx=3, so that's fetching two ULLs too > far. > > > + goto out; \ > > + idx++; \ > > + } \ > > + \ > > + sz = min(idx * BITS_PER_LONG + __ffs(MUNGE(tmp)), sz); \ > > +out: \ > > + sz; \ > > +})
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