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Milestones #6

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acmnpv opened this issue Jan 29, 2015 · 6 comments
Open

Milestones #6

acmnpv opened this issue Jan 29, 2015 · 6 comments

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@acmnpv
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acmnpv commented Jan 29, 2015

Hej,
I have recently seen the milestones for the development and was wondering why you want to kill the optimisation for the tools?

Thanks for answering

Paul

@amrein
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amrein commented Jan 29, 2015

Hi,
Because its a particularly bad idea to trade accuracy for speed in the tools.
They are fast enough without optimizations. One could discuss -O1 and for some compilers -O2.
But -O3 or -xhost is a very bad idea.

@amrein amrein added this to the Q Version 5.8 milestone Jan 29, 2015
@acmnpv
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acmnpv commented Jan 29, 2015

Ok, I will make the test to see if there are differences between the different optimisations.

@esguerra
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Just echoing what Beat points out from the standard from gcc:

"-O0 Reduce compilation time and make debugging produce the expected results. This is the default. "

https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html

@esguerra
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Reading a bit further:
"-Og Optimize debugging experience. -Og enables optimizations that do not interfere with debugging. It should be the optimization level of choice for the standard edit-compile-debug cycle, offering a reasonable level of optimization while maintaining fast compilation and a good debugging experience."

@acmnpv
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acmnpv commented Jan 29, 2015

Sure, for debugging I have the optimisations turned off. But I just made two versions of Qfep, one with -O3 in gfortran and one with -O0, and both are giving identical results.
So I really don't get what is this about. If you are having issues with optimised binaries, please tell me and I can fix the underlying bugs.

@amrein
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amrein commented Jan 29, 2015

Absolutely, and what about the other tools, did you try them with different architectures (eg the same executable on akka+abisko+triolith+tintin)?
And more importantly: Would you mind to tell us, what the timing differences you obtaind are?

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