[gmx-developers] hidden compiler flags in 4.6?

[Roland Schulz]

On Tue, Feb 5, 2013 at 2:58 PM, Szilárd Páll <szilard.pall at cbr.su.se> wrote:

>  For all developers out there: RFC.
>
> I hope you do realize that the issues we are discussing are not if-s and
> when-s and you'll face them as soon as you want to add/remove/change a
> compiler flag!
>
sure. It is even clearly documented in the commit message.

>
>  I'll have a look at the discussion, but I'll need quite some time for
> that as it very lengthy and contains a long, slightly unrelated, debate.
>
>  Note that I'm not talking about some magic override, but simply the
> ability to go to the flags and remove e.g. the "-ip" icc flag which I know
> that it can in some cases cause performance regression.
>
That's the problem. It is not that easy. I originally made a more
complicated suggestion which would have allowed overwrite but it would have
been very complicated. So please take the time to read everything AND make
a specific suggestion of how to change it. And also keep in mind that we
usually don't change behavior after a release.


>  In my eyes, reviewing and changing flags is much more important than the
> consistency of acceleration flags across cmake reruns, that's why I find it
> unfortunate that the build system got crippled in an attempt to fix that
> issue.
>
That wasn't the only problem. It wasn't consistent at all.


>
>>
>>>    and adding or overriding should be possible through a single
>>> command-line invocation.
>>>
>>> More concretely IMO what we need is:
>>> - A summary printed or at least some read-only advanced variables so
>>> that one does not need to run e.g "mdrun -version" to know what flags are
>>> used;
>>>
>>  I was (and still am) all for the summary. I really liked Teemu's start
>> of it. But it got cut because of time. Not sure it would be a good idea to
>> print just the flags without having a full summary. I think having
>> read-only variables is very confusing.
>>
>
>  I see your point, but you have yet to reply to my criticism on the fact
> that *it is impossible to at least check what flags are being used* and
> that is a major flaw.
>
Like I said I was hoping for the summary.


>   - An intuitive and consistent way to add/change the flags, what the
>>> user wants is simple, but currently requires a set of strange steps: enable
>>> skipping GROMACS flags, copy the printed flags, remove cache, re-run cmake
>>> with the copied flags.
>>>
>>  No need to remove the cache.
>>
>
>  Fine, remove that step, but you've to add two more instead:
> - check default CMake flags;
> - re-add those when setting flags manually
>
>  Again, I would very much appreciate of you or others developers would
> actually comment on the issue in question: the usability concerns around
> this rather long, complicated, and error-prone set of steps required just
> to change a flag -Foo to -Bar.
>
Please not that it is still better than some other compiler/linker flags
which can't be changed at all. E.g. OpenMP flags are autodected and can't
be changed at all (unless you change the cmakelists code). The same is true
for any linker flags (e.g. bug 911). To repeat myself: I would have liked
to have a solution which would have made overwriting easy and which would
have contained a summary. But that was the solution which seemed best with
the available time. Please also note that these bugs are 3 months old.
Everyone had plenty of time to come up with a better solution in those 3
months.

Roland


>
>  Cheers,
> --
> Szilárd
>
>
>
>>
>>  Roland
>>
>>
>>>    It might be a good idea to override everything or nothing regardless
>>> whether it's GROMACS or CMake flags.
>>>
>>>  Cheers,
>>> Szilard
>>>
>>>
>>>>  Roland
>>>>
>>>>
>>>>
>>>>>
>>>>>  Cheers,
>>>>>  --
>>>>> Szilárd
>>>>>
>>>>
>>>>
>>>>
>>>>  --
>>>> ORNL/UT Center for Molecular Biophysics cmb.ornl.gov
>>>> 865-241-1537, ORNL PO BOX 2008 MS6309
>>>>
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>>>
>>>
>>
>>
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>> 865-241-1537, ORNL PO BOX 2008 MS6309
>>
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>
>


-- 
ORNL/UT Center for Molecular Biophysics cmb.ornl.gov
865-241-1537, ORNL PO BOX 2008 MS6309
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