[R-SIG-Mac] Multi-thread R processes performance on 8-core Mac-Pro

[Sean Davis]

On Wednesday 18 April 2007 02:48, Marra, David wrote:
> Everyone,
>
> I am running R 2.4.1 on the new 8-core Mac Pro with the parSapply
> function from the Snow package. Tests using 2,4, and 8 threads with
> makeCluster() yield somewhat disappointing results. The 4 thread process
> is fastest. With 8 threads, all the cores max out at about 70% power,
> and even then it is slower than the 4 thread process which maxes out the
> 4 threads at about 90-95%. This suggests the additional 4 cores on the
> Mac Pro do not improve performance in an embarrassingly parallel R/Snow
> environment...
>
> The function I tested in parSapply runs a regression (a call to "lm"). I
> am using Snow/rpvm package combination. There is no issue of limited
> memory. There are over 3 gigs of free RAM in the tests.
>
> Does anyone have suggestions as how to get more power out of a
> multi-core Mac Pro machine and/or have 4-core/8-core R multi-thread
> computing performance benchmarks/experiences to share?

David,

Under snow/rpvm, pure CPU usage is not the only variable that goes into 
efficiency.  There are potentially interprocess communication, disk I/O, 
memory utilization, and perhaps other variables that ultimately determine the 
efficiency of parallel code.  Assuming that your test results are correct, it 
might be the case that the CPU is being limited by one or more of the other 
variables.

Sean