CFD Online Logo CFD Online URL
Home > Forums > General Forums > Main CFD Forum

Fluent/CFX & Win OS: 30% slow down with MS HPC Pack 2016

Register Blogs Members List Search Today's Posts Mark Forums Read

LinkBack Thread Tools Search this Thread Display Modes
Old   January 31, 2020, 15:26
Default Fluent/CFX & Win OS: 30% slow down with MS HPC Pack 2016
Join Date: Jul 2011
Posts: 53
Rep Power: 14
SLC is on a distinguished road
Iím posting this in the general forum as opposed to an ANSYS related one because I suspect this is an issue with the job scheduler found in the Microsoft HPC Pack 2016.

HPC Pack 2016 is based on MS MPI. That in itself is not a problem, as it is a modern MPI platform that supports fast interconnects.

I can run both CFX and Fluent locally on a compute node (dual socket, 16 core CPUs for a total of 32 cores) using Intel MPI, Platform/IBM MPI, or MS MPI with great success, giving me the expected performance. This is running Windows Server 2019.

However, as soon as I run via the job scheduler in HPC Pack 2016 on that same node, my CFX and Fluent runs see a 30% slow down. This slow down is the same if Iím running directly on the head node (with the head node also configured as a compute node), or if Iím running on a separate compute node connected via HDR infiniband.

If I, for example, run Fluent directly on the node, and start the session using msmpi, I get 100 % performance. If I start the session using the job scheduler and connect to a head node (also using msmpi) but run the simulation on that same compute node,, the simulation speed drops by 30%.

Has anyone encountered the similar problem?
SLC is offline   Reply With Quote

Old   February 1, 2020, 12:32
Join Date: Jul 2011
Posts: 53
Rep Power: 14
SLC is on a distinguished road
I appear to have solved my issue. I suspected it relates to affinity settings for the MS MPI, something which we can’t easily change when submitting runs to the Job Scheduler through either Fluent Launcher or CFX Solver Manager.

The quick fix is to ensure that the “exclusive” flag in the HPC Pack 2016 job template is set to “true.”. Then you get full performance as expected
SLC is offline   Reply With Quote


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On

Similar Threads
Thread Thread Starter Forum Replies Last Post
Ansys Licence Serve on Ubuntu 16.04 LTS david.pasquale ANSYS 2 January 20, 2017 11:52
Slow Cases using HPC and PBS job scheduler Alhasan OpenFOAM Running, Solving & CFD 5 February 1, 2015 11:07
need MS HPC Pack to run in "parallel" mode Chris Lee SU2 0 November 24, 2014 20:05
Can we merge HPC Pack licenses? Phillamon FLUENT 0 January 24, 2014 02:59
Microsoft HPC Pack 2008 Tool Pack (LINPACK) jemyungcha Hardware 1 October 22, 2011 18:21

All times are GMT -4. The time now is 08:19.