From: Andy Shevchenko > Sent: 01 February 2021 13:49 > > On Sat, Jan 30, 2021 at 11:17:18AM -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. > > Would be nice to have the examples how it reduces the actual code size (based > on the existing code in kernel, especially in widely used frameworks / > subsystems, like PCI). I bet it makes the kernel bigger but very slightly faster. But the fact that the wrappers end up in the i-cache may mean that inlining actually makes it slower for some calling sequences. If a bitmap fits in a single word (as a compile-time constant) then you should (probably) be using different functions if you care about performance. David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
