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Re: GNU C library's libmvec and the GNU Compiler *Collection*.
- From: Toon Moene <toon at moene dot org>
- To: gcc at gcc dot gnu dot org
- Date: Wed, 6 Jan 2016 23:48:29 +0100
- Subject: Re: GNU C library's libmvec and the GNU Compiler *Collection*.
- Authentication-results: sourceware.org; auth=none
- References: <568D611F dot 4020805 at moene dot org>
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