R sys.child中的system.time和parallel包为0 [英] system.time and parallel package in R sys.child is 0

问题描述

我想在R中使用system.time来获取多核函数上的总CPU时间.问题在于，system.time显然无法捕获并行程序包所产生的子进程所花费的CPU时间.

I would like to use system.time in R to get the total CPU time on a multicore function. The problem is that system.time does obviously not capture CPU time spend by the child processes spawned by the parallel package.

library(doParallel)
cl <- makeCluster(2)
registerDoParalllel(2)
timings <- system.time(foreach(i = 1:2) %do% rnorm(1e8))

时间然后看起来像这样

> timings
   user  system elapsed 
 16.883   5.731  22.899 

计时加起来.现在，如果我使用并行处理:

The timings add up. Now if I use parallel processing:

timings <- system.time(foreach(i = 1:2) %dopar% rnorm(1e8))
> timings
   user  system elapsed 
  2.445   3.410  20.347 

用户和系统时间仅捕获主进程.专门查看时间[4]和[5]，可以发现user.child和sys.child时间均为0.

The user and system time are only capturing the master process. Specifically looking at the timings[4] and [5] shows me that the user.child and sys.child times are 0.

在并行处理中，如何测量R中的CPU总时间?

What do I have to do to measure total CPU time in R on parallel processing?

注意:将集群启动代码移入system.time调用没有任何作用.

Note: Moving the cluster startup code into the system.time call did not make a difference.

> sessionInfo()
R version 3.3.2 (2016-10-31)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Debian GNU/Linux 8 (jessie)

other attached packages:
[1] doParallel_1.0.10 iterators_1.0.8   foreach_1.4.3    

推荐答案

@ chinsoon12为我指明了正确的方向.仅当通过registerDoParallel创建集群时，才会填充user.child和sys.child.

@chinsoon12 pointed me in the right direction. user.child and sys.child are only populated when the cluster is created by registerDoParallel, e.g.

registerDoParalllel(cores = 2)
timings <- system.time(foreach(i = 1:2) %dopar% rnorm(1e8))

        user.self sys.self elapsed user.child sys.child
timings     0.429    1.978  19.378      9.818     1.386

这就是为什么它与doMC开箱即用的原因，我没有通过cl变量手动启动和停止集群.

This is why it worked out of the box with doMC where I did not manually start and stop the cluster via the cl variable.

这篇关于R sys.child中的system.time和parallel包为0的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！