Minimize communication barriers

[rmontuoro]

Description

This PR starts to implement changes discussed in issue #1118 with the purpose of eliminating unnecessary communication barriers to attempt improving runtime performance of MAPL-based applications.

Related Issue

See issue #1118.

Motivation and Context

Improving runtime performance of MAPL-based applications.

How Has This Been Tested?

These changes have been tested on NOAA platforms with Intel 18.0.5.274 and Intel MPI 2018.0.4.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Trivial change (affects only documentation or cleanup)

Checklist:

• I have tested this change with a run of GEOSgcm (if non-trivial)
• I have added one of the required labels (0 diff, 0 diff trivial, 0 diff structural, non 0-diff)
• I have updated the CHANGELOG.md accordingly following the style of Keep a Changelog

[tclune]

@rmontouro - If you have any performance numbers indicating a measurable difference, it would be nice to capture them here. Nothing fancy just a % change for this layer or UFS as a whole.