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Where "cpus" are mentioned, read "cores". I'll try to make this clearer at some point.

Introduction

When Gridengine (e.g., 8.1.9) calculates cpu usage information, it is done based on slots used and either cpu time or wallclock time. This works if each slot corresponds to a single cpu. But, if more than one cpu is allocated to a slot, this calculation does not give the desired usage information.

For the purposes of this article:

  • execd_params is configured with ACCT_RESERVED_USAGE=true and SHARETREE_RESERVED_USAGE=true so that wallclock time rather than cpu time is used

  • cpus are a dedicated resource managed by a consumable

  • jobs request the number of cpus for each slot

with the goal of calculating cpu usage as:

cpu = wallclock * nslots * ncpus_per_slot

Usage

The complex used to track the number of cpus used per slot is specified in the execd_params with SLOT_MULTIPLIER_NAME. E.g.

execd_params	SLOT_MULTIPLIER_NAME=ncpus

The complex would be defined as:

ncpus               ncpus       INT       <=    FORCED      YES        0        1000

A queue would be configured with:

complex_values        ncpus=4
  • 4 cpus allocatable from this queue

So, a job request for 4 slots X 16 cpus would be:

#$ -pe dev 4
#$ -l ncpus=16

and a run of 30s would amount to:

cpu = 30 * 4 *16 = 1920

versus what is currently returned:

cpu = 30 *4 = 120

Implementation

Changes

source/libs/sgeobj/sge_conf.h:

  • add mconf_get_slot_multiplier_name() declaration

source/libs/sgeobj/sge_conf.c:

  • set slot_multiplier_name static variable to hold value set in execd_params SLOT_MULTIPLIER_NAME
  • implement mconf_get_slot_multiplier_name()

source/daemons/execd/load_avg.h:

  • augment build_reserved_usage() declaration to accept reference to job

source/daemons/execd/load_avg.c:

  • augment build_reserved_usage() to accept reference to job
  • enhance build_reserved_usage() to get slot multiplier and use it when calculating cpu usage
  • add get_slot_multiplier() static function get the multiplier value if defined, or 1.0 otherwise
  • update calculate_reserved_usage() to get job reference and provide it when calling build_reserved_usage()

source/daemons/execd/reaper_execd.c:

  • update build_derived_final_usage() to provide job reference when calling build_reserved_usage()

Patch files (based off of https://arc.liv.ac.uk/downloads/SGE/releases/8.1.9/):

Summary

Changes to the code are minimal. The highlights are:

  • change the signature of the build_reserved_usage() function to take a job reference so that the consumable information can be obtained
  • update build_reserved_usage() to use the slot multiplier value

Conclusion

These changes make it possible to account for the number of cpus per slot which is critical to calculating cpu usage by wallclock.

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