Chris Douglas commented on YARN-3612:

bq. Moreover, I have not added the config as I do not see anyone disabling it. 
Thoughts ?

The config change could be useful for MR jobs that want to avoid the CPU 
overhead. Suggest changing calls to {{nanoTime}} from {{currentTimeMillis}} 
since it's measuring durations.

+1 overall, even without the change to {{Task}}.

> Resource calculation in child tasks is CPU-heavy
> ------------------------------------------------
>                 Key: YARN-3612
>                 URL: https://issues.apache.org/jira/browse/YARN-3612
>             Project: Hadoop YARN
>          Issue Type: Bug
>    Affects Versions: 2.7.0
>            Reporter: Todd Lipcon
>              Labels: BB2015-05-RFC, performance
>         Attachments: MAPREDUCE-4469.patch, MAPREDUCE-4469_rev2.patch, 
> MAPREDUCE-4469_rev3.patch, MAPREDUCE-4469_rev4.patch, 
> MAPREDUCE-4469_rev5.patch, YARN-3612.01.patch, YARN-3612.02.patch
> In doing some benchmarking on a hadoop-1 derived codebase, I noticed that 
> each of the child tasks was doing a ton of syscalls. Upon stracing, I noticed 
> that it's spending a lot of time looping through all the files in /proc to 
> calculate resource usage.
> As a test, I added a flag to disable use of the ResourceCalculatorPlugin 
> within the tasks. On a CPU-bound 500G-sort workload, this improved total job 
> runtime by about 10% (map slot-seconds by 14%, reduce slot seconds by 8%)

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