On Wed, Aug 20, 2025 at 04:01:22PM +0200, Juergen Gross wrote: > On 20.08.25 15:42, Yury Norov wrote: > > On Tue, Aug 19, 2025 at 04:12:11PM -0700, Sean Christopherson wrote: > > > On Sat, 19 Jul 2025 21:58:45 -0400, Yury Norov wrote: > > > > Use find_nth_bit() and make the function almost a one-liner. > > > > > > Applied to kvm-x86 misc, thanks! > > > > > > P.S. I'm amazed you could decipher the intent of the code. Even with your > > > patch, it took me 10+ minutes to understand the "logic". > > > > Thanks Sean. :) > > > > > [1/1] kvm: x86: simplify kvm_vector_to_index() > > > https://github.com/kvm-x86/linux/commit/cc63f918a215 > > Is this really correct? > > The original code has: > > for (i = 0; i <= mod; i++) > > (note the "<="). > > So it will find the (mod + 1)th bit set, so shouldn't it use > > idx = find_nth_bit(bitmap, bitmap_size, (vector % dest_vcpus) + 1); > > instead? > > My remark assumes that find_nth_bit(bitmap, bitmap_size, 1) will return the > same value as find_first_bit(bitmap, bitmap_size). find_nth_bit indexes those bits starting from 0, so find_nth_bit(bitmap, nbits, 0) == find_first_bit(bitmap, nbits) find_nth_bit(bitmap, nbits, 1) == find_next_bit(bitmap, nbits, find_first_bit(bitmap, nbits)) And so on. Check test_find_nth_bit() for the examples. Also, bitmap_size has a different meaning, so let's refer 'nbits' instead.
