parallel SNOW slower than single core?
I'm not surprised -- you're doing a fairly trivial calculation so the overhead of setting up the parallelization is likely more than the benefit from halving the computation time. Do it on a larger calculation and I imagine the performance will be better -- I might just be pulling this out of thin air, but I think I remember reading slides from Luke Tierney saying one had to be adding vectors of size
= 30k or so for parallelization to have a meaningful benefit.
Obviously sizes will be lower for operations more expensive than addition. Michael
On Thu, Aug 2, 2012 at 1:13 PM, Jie <jimmycloud at gmail.com> wrote:
Dear All,
I am learning parallel in R and start with the package "snow". I did a test
about running time and the parallel version is much slower than the regulat
code. My laptop is X200s with dual core intel L9400 cpu.
Should I make more clusters than 2? Or how to improve the performance?
# install.packages("snow")
library(snow)
cl <- makeCluster(2)
t1 <- proc.time()
a <- c()
for (i in 1:1000)
{
a[i] <- sum(parSapply(cl, 1:15, get("+"), 2))
}
proc.time()-t1
t2 <- proc.time()
a <- c()
for (i in 1:1000)
{
a[i] <- sum(sapply(1:15, "+", 2))
}
proc.time()-t2
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