Re: sustained number crunching

On 2011-10-20 17:14:13 -0300, Paul Anton Letnes said:

On 20.10.11 22:01, tholen@xxxxxxxxxxxx wrote:
Not strictly a Fortran question, but because Fortran is good for
sustained number crunching applications, I figure the relevant
expertise would be in this newsgroup.

Are Intel Xeon processors generally better for sustained number
crunching than Intel i3/i5/i7 processors? I see that the latter
processors have a turbo boost mode that can temporarily increase
the clock from something like 2.3 GHz to 3.4 GHz, which is fine
for applications that need short bursts of extra computing power,
but what about sustained number crunching (hours to days)?

The question is partly motivated by a frustrating experience I'm
having with running a number cruncher on a laptop with a Core 2
Duo processor and Fedora 14, with the program having been built
using gfortran. Once the CPU temperature hits a bit over 140 F
some CPU throttling application kicks in and slows down the
processor from 2.5 GHz to 800 MHz until the CPU temperature drops
to around 124 F. But as near as I can tell from Intel tech
specs, the processor (T9300) is rated at something like 95 C or
100 C, so I don't know why CPU throttling is kicking in around
60 C, and so far my attempts to change the behavior by modifying
the settings in a cpuspeed configuration file have failed.

Feel free to comment about AMD processors for sustained number
crunching. I don't have a lot of personal experience with them.

I'd generally recommend keeping the CPU cool, and not using a laptop if possible. The reason is simply that if you keep it cooler, it will last longer. I've heard this from people keeping logs of temperatures in clusters; statistically, the nodes having the highest temperature break down first (CPU or motherboard). Also, the highest rated temperature may not be recommendable for sustained use. I see my own laptop temporarily going above 90 C, but it drops again as the fan hits the max.

I'd recommend using a desktop/cluster (over SSH) if at all possible - I do this to some extent myself, and it generally works reasonably well. Synchronization tools like unison and version control software like hg and/or git make life easier.

Cheers
Paul

PS:
What make is your laptop? It sounds like I don't want to buy one.

My naive reading of the publicity puffery left me with the impression that
turbo boost was for times when only one core of a multi core chip was active.
There the increase is more like from 3.0 to 3.3.

I have a Mac Pro that does not increase its fan speeds for OpenMP runs that
show all 6 cores hyperthreaded for 1200% cpu that works out to about a 7+
times improvement on the same code single threaded. I expect that commodity
laptops are designed to keep one processor cool while surfing the web so
they heat up under load.


.

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