simon.urbanek at r-project.org
Fri Oct 30 16:29:58 CET 2009
On Oct 30, 2009, at 10:30 , Anirban Mukherjee wrote:
> Hi Simon,
> I found some threads in which you discussed the Nehalem processors
> vis-a-vis speedups in R (on Mac). I have to decide between getting a
> Core 2 Duo 3.33 ghz and the Core i7 2.8 ghz iMac. The critical part
> of my code comes down to about 20 megs with heavy (5 to 10 hours) of
> computation (all in memory, no disk access). The function is highly
> non-linear, so its just a whole bunch of BFGS or Nelder-Mead steps
> to find the maximum. I could not see any performance gain from using
> foreach: its very hard to parallelize much in the problem.
In that case I don't think you can use the real power of i7 which lies
in up to 8 parallel HTs (with i5 you get 4 regular cores w/o HT and
C2D gives you 2). I'm not sure whether the memory will have a big
impact. On Nehalems the impressive part is that it can feed the HTs
fast enough (which was not the case with the previous archs) - but
that doesn't matter for you since you won't use them. At least the
Harpertowns were pretty good at feeding up to 6 cores so I didn't see
a big difference. However, Harpertown was still the high-end line, so
I'm not sure how it compares to C2D memory throughput. (I was
impressed by the performance of C2D in my MBP when you omit the fact
that it's just two cores).
If you can send me a working example of your code I can run it on C2D
and Nehalem machines to give you an idea how they compare ...
> I am tempted by the improved memory subsystem. But can't see any
> other benefits of the i7. Any thoughts on likely performance
> differences. I would love to get my hands on a core i7 to actually
> test for myself, but I don't know anyone here who has one. More than
> the 400 odd extra bucks for the i7, I don't want to wait till end of
> Nov (it takes even longer to the get the machines to Singapore),
> unless there is a reason to.
The i5/i7 iMacs are not shipping here yet, either, so it will take a
few weeks until there is some hope of hands-on results ...
> Any comments/pointers would be deeply appreciated. Thanks!
> PS: Feel free to add R-sig-mac to the reply list if you feel others
> might be interested in the same problem. I assume at least a few
> others will be contemplating new iMac purchases and will encounter
> the "is it worth it" question in the context of R.
Thanks, CCing ...
> Anirban Mukherjee | Assistant Professor, Marketing | LKCSB, SMU
> 5056 School of Business, 50 Stamford Road, Singapore 178899 |
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