R％多巴％比％do％慢

Question

我正在尝试运行％dopar％的小测试，它总是变慢。这里是一些虚拟代码和输出。我在win7x64核心i7-2600k上运行它...

library(foreach)
library(doSNOW)
registerDoSNOW(makeCluster(3, type = "SOCK"))

N <- 3*(10^4)

system.time(foreach(i = 1:N) %do% {sum(rnorm(N))})
system.time(foreach(i = 1:N) %dopar% {sum(rnorm(N))} )

这是输出：

> system.time(foreach(i = 1:N) %do% {sum(rnorm(N))})
 user  system elapsed 
90.39    0.00   90.42 

> system.time(foreach(i = 1:N) %dopar% {sum(rnorm(N))} )
user  system elapsed 
17.00    0.89  177.11