[Beowulf] Gentoo in the HPC environment

Prentice Bisbal prentice.bisbal at rutgers.edu
Tue Jul 1 09:51:58 PDT 2014

On 07/01/2014 12:35 PM, Jonathan Aquilina wrote:

> I think my question though is this. can one see negative impacts if the
> compiler gets upgraded regardless of if its gcc or intel.
If you're talking about the distro-provided compiler, no. They are 
usually tested well by the distro maintainer, and any updates within a 
distro's release version will only be maintenance security and bug fixes.

Now if you're talking about installing GCC 4.7.2 on your own and then 
updating to 4.8 or doing something similar with the Intel Compilers or 
Portland Compilers, it's always a good idea to install the different 
versions in their own install tree and keep the old versions around. 
It's quite common for new compilers to have new bugs. I never delete old 
versions of compilers. In academia, researcher like to be able to 
reproduce their work, or compare their results using a new compiler to 
an old compiler. Removing the old version breaks that. If a compiler 
version is really, really old, I'll ask my users if it's safe to remove it.

>> On 07/01/2014 12:17 AM, Matt Wallis wrote:
>>> On 01/07/14 13:45, Jonathan Aquilina wrote:
>>>> This question probably sounds like a stupid one, but what difference
>>>> in an
>>>> HPC environment and to parallel written code does compiler version
>>>> make?
>>> Depends on the day of the week, the processor, the code, and your
>>> cluster really.
>>> Sometimes code from GCC is faster, sometimes code from the Intel
>>> compiler is faster.
>>> Some people write code that only compiles with the Intel compiler, or
>>> link against libraries distributed with the compiler.
>>> Then of course you might have a BlueGene with PPC cores rather than
>>> x86, and while the difference in performance between GCC for PPC and
>>> the IBM XL compilers is slight these days, it wasn't always the case.
>> One of my researchers has found that his code that is integer-heavy runs
>> up to 5x faster on our BG/P when compiled with GCC over the same code
>> compiled with the IBM XL compilers. For floating point heavy codes, the
>> IBM XL compiles produce much faster code.
>>> Intel also distributes highly tuned versions of some maths libraries
>>> with their compilers, and libraries designed for offloading work to
>>> the the Xeon Phi, without recompiling the application.
>>> And then when it comes time to debug why the application doesn't work,
>>> commercial compiler suites often come with very good debugging tools.
>>> Matt.
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