[R] 8 fast or 4 very fast cores?

[Prof Brian Ripley]

On 15/09/2014 11:21, Ben Bolker wrote:
> Leif Ruckman <Leif <at> Ruckman.se> writes:
>
>>
>> I am going to buy a new computer ( Dell workstation T5810 - Windows 8)
>> to work with simulatons in R.
>>
>> Now I am asked what kind of processor I like and I was given two choices.
>>
>> 1. Intel Xeon E5-1620 v3 - 4 cores 3.7 GHz Turbo
>> 2. Intel Xeon E5-2640 v3 - 8 cores 2.6 GHz Turbo
>>
>> I don't know what is better in simulations studies in R, a few very fast
>> cores or many cores at normal speed.
>
>
>    It's **very** hard to answer such general questions reliably, but I'll
> take a guess and say that if you're doing simulation studies you're likely
> to be doing tasks that are easily distributable (e.g. many random
> realizations of the same simulation and/or realizations for many
> different sets of parameter values) and so the more-cores option
> will be a good idea.
>
>    But it's possible that what you mean by "simulation studies" is
> different.
>
>    If you can do some benchmarking of your problems on an existing
> machine that would probably be a good idea.

Unfortunately unless it is of very similar architecture that may not 
help much.

Three issues hard to scale from are the 'Turbo', the hyperthreading of 
modern Xeons and the cache sizes.  Now, I happen to have machines with 
multiple E5-24x0 and E5-26x0 Xeons: both do hyperthreading well, so you 
would have 8 or 16 virtual CPUs and they will give you say 50% increase 
in throughput if all the virtual cores are used.  But you cannot scale 
up from using just one process on one core.

I find it hard to think of tasks where option 1) would have more 
throughput, but if most of the time you are not running things in 
parallel then the higher speed on a single task is a consideration.

>
>    Ben Bolker
>
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-- 
Brian D. Ripley,                  ripley at stats.ox.ac.uk
Emeritus Professor of Applied Statistics, University of Oxford
1 South Parks Road, Oxford OX1 3TG, UK