I got around ~12% gain with -Ofast -mcpu=cortex-a57. Regards, Venkat.
> -----Original Message----- > From: gcc-patches-ow...@gcc.gnu.org [mailto:gcc-patches- > ow...@gcc.gnu.org] On Behalf Of Dr. Philipp Tomsich > Sent: Thursday, June 25, 2015 9:13 PM > To: Kumar, Venkataramanan > Cc: Benedikt Huber; pins...@gmail.com; gcc-patches@gcc.gnu.org > Subject: Re: [PATCH] [aarch64] Implemented reciprocal square root (rsqrt) > estimation in -ffast-math > > Kumar, > > what is the relative gain that you see on Cortex-A57? > > Thanks, > Philipp. > > > On 25 Jun 2015, at 17:35, Kumar, Venkataramanan > <venkataramanan.ku...@amd.com> wrote: > > > > Changing to "1 step for float" and "2 steps for double" gives better gains > now for gromacs on cortex-a57. > > > > Regards, > > Venkat. > >> -----Original Message----- > >> From: gcc-patches-ow...@gcc.gnu.org [mailto:gcc-patches- > >> ow...@gcc.gnu.org] On Behalf Of Benedikt Huber > >> Sent: Thursday, June 25, 2015 4:09 PM > >> To: pins...@gmail.com > >> Cc: gcc-patches@gcc.gnu.org; philipp.toms...@theobroma-systems.com > >> Subject: Re: [PATCH] [aarch64] Implemented reciprocal square root > >> (rsqrt) estimation in -ffast-math > >> > >> Andrew, > >> > >>> This is NOT a win on thunderX at least for single precision because > >>> you have > >> to do the divide and sqrt in the same time as it takes 5 multiples > >> (estimate and step are multiplies in the thunderX pipeline). Doubles > >> is 10 multiplies which is just the same as what the patch does (but > >> it is really slightly less than 10, I rounded up). So in the end this > >> is NOT a win at all for thunderX unless we do one less step for both single > and double. > >> > >> Yes, the expected benefit from rsqrt estimation is implementation > >> specific. If one has a better initial rsqrte or an application that > >> can trade precision for execution time, we could offer a command line > >> option to do only 2 steps for doulbe and 1 step for float; similar to - > mrecip-precision for PowerPC. > >> What are your thoughts on that? > >> > >> Best regards, > >> Benedikt
