Messages in this thread | | | From | Nick Desaulniers <> | Date | Thu, 1 Sep 2022 10:06:48 -0700 | Subject | Re: [PATCH v6 0/2] x86/asm/bitops: optimize ff{s,z} functions for constant expressions |
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On Thu, Sep 1, 2022 at 7:19 AM Yury Norov <yury.norov@gmail.com> wrote: > > On Thu, Sep 01, 2022 at 07:30:10PM +0900, Vincent MAILHOL wrote: > > On Tue. 1 sept. 2022 at 12:49, Yury Norov <yury.norov@gmail.com> wrote: > > > 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. > > > > Hi Yury, > > > > My patch only takes care of the x86 architecture. > > OK, I just realized that you started submitting this at least back in May. > > For me, v6 is good enough and well-described. So, for the series: > Reviewed-by: Yury Norov <yury.norov@gmail.com> > > How are you going to merge it? If you haven't a specific tree in mind > already, I can take it in my bitmap tree because ffs and ffz are closely > related to find_bit() functions.
Unless Boris feels strong enough to nack the series, I think Yury accepting the series is the way to go. -- Thanks, ~Nick Desaulniers
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