On Mon, Feb 01, 2021 at 04:02:30PM +0000, David Laight wrote: > 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. Isn't this patch series exactly about it? -- With Best Regards, Andy Shevchenko
