[R-sig-hpc] Difference between PSOCK and MPI?

[Simon Urbanek]

On Apr 11, 2013, at 2:23 PM, Marius Hofert wrote:

> 
> 
> Dirk Eddelbuettel <edd at debian.org> writes:
> 
>> On 9 April 2013 at 23:24, Marius Hofert wrote:
>> | What are the main differences (advantages/drawbacks) between parallel's makeCluster(,
>> | type="PSOCK") and makeCluster(, type="MPI")? According to
>> | http://cran.r-project.org/web/views/HighPerformanceComputing.html, MPI has
>> | become the 'standard', although the default type of makeCluster() is "PSOCK". Is
>> | "PSOCK" more compatible in that it does not need an installation such as
>> | (open)MPI? slower/faster/no difference?
>> 
>> You don't want PSOCK.  
>> 
>> It is the lowest common demoninator which even works (for various definitions
>> of "work") on Windoze.
> 
> Hi Dirk,
> 
> thanks for helping. Indeed, we don't want that. The reason I was asking for is
> the following: I am writing a package (jointly with Martin) where we make use of
> makeCluster(). The 'natural' default would be to use the default of the
> 'type' argument ("PSOCK") and leave it up to the user to decide if he wants to replace
> it by "MPI". On the other hand, one could make "MPI" the default advocating
> 'good practice'. Since we are unsure, I thought I ask about the differences
> between the two to get a better feeling for what a good default would be.
> 

One thing to consider for a package is that MPI is probably not available in the majority of cases. In fact, MPI back-end is not even available in parallel by default (it routes to "snow" strangely ...). Although PSOCK is not the best performant back-end it is reasonably easy to setup so I would certainly keep it as default. If someone knows how to setup MPI then they do know how to set the optional argument, not the other way around ;).

Cheers,
Simon



>> 
>> 
>> As your mail address reveals that you are coming from a serious place, 
> 
> :-)
> 
>> you should look into MPI.
> 
> we always used it, that's why it became the (internal) default so far. 
> 
> Cheers,
> 
> Marius
> 
> 
>> Or just use N core machines, where N is a big as your grant allows.
>> 
>> Dirk
> 
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