Update description of cores, memory, job_cpu and job_mem parameters (#676)

Author: maneesh29s

dask_jobqueue/core.py

@@ -25,9 +25,12 @@
 
 job_parameters = """
     cores : int
-        Total number of cores per job
+        Total number of CPU cores on which all worker threads inside a job will run.
+        The number of threads per worker process are determined using the formula ``cores / processes``.
+        Used by job queuing system by default as amount of CPUs per job.
     memory: str
-        Total amount of memory per job
+        Total amount of memory to be used by all workers inside a job.
+        Used by job queuing system by default as amount of memory per job.
     processes : int
         Cut the job up into this many processes. Good for GIL workloads or for
         nodes with many cores.

dask_jobqueue/slurm.py

@@ -166,10 +166,11 @@ class SLURMCluster(JobQueueCluster):
     walltime : str
         Walltime for each worker job.
     job_cpu : int
-        Number of cpu to book in SLURM, if None, defaults to worker `threads * processes`
+        Number of CPUs to request in SLURM for each job.
+        This option might be useful to request more CPUs than total number of worker threads
+        for some complex non-python code. If None, defaults to ``cores``.
     job_mem : str
-        Amount of memory to request in SLURM. If None, defaults to worker
-        processes * memory
+        Amount of memory to request in SLURM for each job, If None, defaults to ``memory``.
     job_extra : list
         Deprecated: use ``job_extra_directives`` instead. This parameter will be removed in a future version.
     job_extra_directives : list