topic Re: Ifort vs ifx speed issue in Intel® Fortran Compiler

Ifort vs ifx speed issue

Umar__Sait — Sat, 03 Jul 2021 13:00:49 GMT

I have been using ifort version 19.1.3.304 and just updated to OneAPI ifort version 2021.3.0
and ifx version 2021.3.0 Beta. Doing some speed test of my production code that uses openmp I find that ifort classic is running much faster than the ifx.

ifort 19.1.3.304 and ifort 2021.3.0 run at exactly the same speed:

real    153m58.297s
user    3150m35.557s
sys     15m18.230s

However, ifx runs at:

real    237m0.759s
user    4655m44.994s
sys     20m52.255s

The compiler flags are -O3 -xHost -qopenmp for both runs. This is on dual cpu dell precision 7920 with Intel(R) Xeon(R) Gold 6256 CPU @ 3.60GHz. The library paths for both compilations point to the same place (is this correct?) in my makefiles. Am I doing something wrong or does the beta version have some debug features etc that is slowing the runs down. Thanks!

Re: Ifort vs ifx speed issue

Bernard — Mon, 05 Jul 2021 13:42:03 GMT

@Umar__Sait

For this kind of comparison VTune profiler should have been used. The timing results as posted by you are too abstract to reveal the exact reason of apparent much worse performance of the code compiled by the 'ifx'.

Re: Ifort vs ifx speed issue

Umar__Sait — Mon, 05 Jul 2021 13:53:47 GMT

Yes, naturally, but I found the following statement from Intel:

"ifort will remain Intel’s recommended production compiler until ifx has performance and features superior to ifort. In the future, when ifx functionality and performance equivalence or better against ifort is achieved, Intel may suggest using ifx, instead of, ifort for performance critical applications."

Re: Ifort vs ifx speed issue

Bernard — Mon, 05 Jul 2021 14:11:23 GMT

So the Intel answer posses some degree of clarification. More in-depth "digging" (as I stated) would require a profiler and combination of sampling and counting mode.

Re: Ifort vs ifx speed issue

Steve_Lionel — Mon, 05 Jul 2021 14:24:12 GMT

The critical words in the text you quoted are "until" and "In the future". At present, ifx is an early beta compiler whose performance is definitely NOT superior to ifort. Feel free to try ifx, but ifort remains the production compiler of choice for now.

Re: Ifort vs ifx speed issue

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