GNU C library's libmvec and the GNU Compiler *Collection*.

[Toon Moene]

On 01/06/2016 07:46 PM, Toon Moene wrote:

> [ This is relevant for our code, because just the switch to *actual*
>    single precision exp/log/sin/cos implementations in glibc's libm
>    resulted in a decrease of the running time of our weather forecasting
>    code by 25 % (this was in glibc 2.16, IIRC). ]

The reference for this is (on an Ivy Bridge system):

https://gcc.gnu.org/ml/gcc-help/2013-01/msg00175.html

"I have made a home-build glibc-2.17 (on a core-avx system). It works 
great - linking against it (instead of using the current 
Debian-Testing's eglibc-2.13) brought the wall-clock time of my weather 
forecasting job down from 3:35 hours to 2:45 (mostly due to a more 
efficient implementation of powf, expf and logf)."

So, in minutes of compute time:

This is (215-165) / 215 = 0.23 (23 %). However, that number included a 
part that ran for an hour (60 minutes) in double precision.

Excluding that we get (155 - 105) / 155 = 0.32 (32 %) improvement in 
performance for the single precision part of our weather forecasting code.

Kind regards,

-- 
Toon Moene - e-mail: toon@moene.org - phone: +31 346 214290
Saturnushof 14, 3738 XG  Maartensdijk, The Netherlands
At home: http://moene.org/~toon/; weather: http://moene.org/~hirlam/
Progress of GNU Fortran: http://gcc.gnu.org/wiki/GFortran#news