Messages in this thread | | | Date | Wed, 31 Aug 2022 20:49:27 -0700 | From | Yury Norov <> | Subject | Re: [PATCH v6 0/2] x86/asm/bitops: optimize ff{s,z} functions for constant expressions |
| |
On Wed, Aug 31, 2022 at 01:54:01AM -0700, Yury Norov wrote: > On Wed, Aug 31, 2022 at 04:57:40PM +0900, Vincent Mailhol wrote: > > The compilers provide some builtin expression equivalent to the ffs(), > > __ffs() and ffz() functions of the kernel. The kernel uses optimized > > assembly which produces better code than the builtin > > functions. However, such assembly code can not be folded when used > > with constant expressions. > > > > This series relies on __builtin_constant_p to select the optimal solution: > > > > * use kernel assembly for non constant expressions > > > > * use compiler's __builtin function for constant expressions. > > > > > > ** Statistics ** > > > > Patch 1/2 optimizes 26.7% of ffs() calls and patch 2/2 optimizes 27.9% > > of __ffs() and ffz() calls (details of the calculation in each patch). > > Hi Vincent, > > Can you please add a test for this? We've recently added a very similar > test_bitmap_const_eval() in lib/test_bitmap.c. > > dc34d5036692c ("lib: test_bitmap: add compile-time optimization/evaluations > assertions") > > Would be nice to have something like this for ffs() and ffz() in > lib/test_bitops.c. > > Please keep me in loop in case of new versions.
Also, what about fls? Is there any difference with ffs/ffz wrt compile time optimizations? If not, would be great if the series will take care of it too.
Thanks, Yury
| |