[Users] -xHost in edison.cfg

[Erik Schnetter]

It's strange that code without "-xHost" does not run on the head node. What
other compiler options are there? The only reason I can see is that the
Intel compiler has been installed in a special way to use additional
compiler flags, and these flags make the code not work any more on Sandy
Bridge.

To my knowledge, the processors accept the same machine instructions. The
CPU tuning might be different.

Running short tests or compiled utilities on the head nodes is very
convenient. I would continue to make sure the code runs everywhere until
there is a proven performance benefit.

-erik


On Sun, Sep 18, 2016 at 2:36 PM, Roland Haas <rhaas at illinois.edu> wrote:

> Hello all,
>
> NERSC's edison cluster specifies -xHost in its cfg file. However login
> nodes and compute nodes are actually different (Sandy Bridge vs. Ivy
> Bridge cpus).
>
> A quick test removing -xHost reveals a possible reason: without -xHost
> the compiled exectuables do not run on the head node. No for the actual
> question: is it worthwhile to claim cross compilation (and the
> requirement to have to specify endianess, type sizes etc manually) to
> possibly gain some more speed?
>
> Given that Ivy and Sandy Bridge are tick and tock I would not expect
> much of a gain (though maybe Ivy Bridge actually offers wider AVX
> instructions?).
>
> At least I will add a comment to edison.cfg explaining why either
> -xHost is used or why a cross compilation is required.
>
> Yours,
> Roland
>
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-- 
Erik Schnetter <schnetter at cct.lsu.edu>
http://www.perimeterinstitute.ca/personal/eschnetter/
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