Github user sryza commented on the pull request:
https://github.com/apache/spark/pull/5063#issuecomment-93058391
My understanding based on the discussion here is that
`spark.mesos.executor.cores` is the number of cores reserved by an executor
*not* for use in running tasks. So if `spark.mesos.executor.cores` is 1,
`spark.task.cpus` is 2, and 3 tasks are running, then a total of 7 cores are
being occupied. The primary use case for setting it to a number different than
1 is that Mesos allows values that are smaller than 1. So, when running
multiple executors per node, someone might set it to .1 in order to avoid
sitting on a bunch of the node's cores.
Did you look at the documentation for the new property? If this wasn't
clear, then we should probably update the doc with a better explanation or link
to relevant Mesos doc.
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