Intel® Fortran Compiler
Build applications that can scale for the future with optimized code designed for Intel® Xeon® and compatible processors.
Announcements
Welcome to the Intel Community. If you get an answer you like, please mark it as an Accepted Solution to help others. Thank you!

libiomp5md.dll performance issue

cabrita__christophe
168 Views

Hello,

We are experiencing a severe performance degradation when upgrading from libiomp5md.dll V5.0.2017.706 (delivered with IntelFortran V2017.5) to libiomp5md.dll V5.0.2018.913 (Fortran V2019.1).

Scenario:

- 2 instances of a multithread 64-bit executable running simultaneously on Windows7 Pro (V6.1 no 7601 : SP1)

- output from OpenMp KMP_AFFINITY=none,verbose:

OMP: Info #212: KMP_AFFINITY: decoding x2APIC ids.
OMP: Info #210: KMP_AFFINITY: Affinity capable, using global cpuid leaf 11 info
OMP: Info #154: KMP_AFFINITY: Initial OS proc set respected: 0-5
OMP: Info #156: KMP_AFFINITY: 6 available OS procs
OMP: Info #157: KMP_AFFINITY: Uniform topology
OMP: Info #179: KMP_AFFINITY: 1 packages x 6 cores/pkg x 1 threads/core (6 total cores)

- Launching 2 instances of the executable with 6 threads per process provokes very slow execution for both processes (approx. 50 times slower than normal). Killing either one of the processes immediately "accelerates" the remaining process.

- Modifying the number of threads per process has the following effect:

- 5 threads: both processes execute rapidly

- 7 threads: both processes execute rapidly, though not quite as rapidly as with 5 threads

- Replacing libiomp5md.dll V5.0.2018.913 with libiomp5md.dll V5.0.2017.706 (no rebuilding of the executables) results in rapid execution is all cases.

 

I have not yet produced a simple minimal executable that reproduces the problem though I will obviously try to if necessary. Before I set about doing so can the Intel support team say if they are any known issues with libiomp5md.dll V5.0.2018.913? Can I supply any more info to help with the diagnosis?

 

Regards,

John Sturton

0 Kudos
5 Replies
Barbara_P_Intel
Moderator
168 Views

Try the current release, 19.0 update 3.  There is fix for the performance degradation of running multiple OpenMP jobs simultaneously.

 

cabrita__christophe
168 Views

Thanks, I will try the 19.0U3 version. Is this fix mentioned in any of the release notes?

Barbara_P_Intel
Moderator
168 Views

It's not in the release notes.

 

cabrita__christophe
168 Views

The 19.0U3 version of libiomp5md.dll (V5.0.2019.109) seems to fix the problem - we now have execution times comparable to those observed when using libiomp5md.dll V5.0.2017.706. Thank you for your help.

For info: We had previously tried with the version of libiomp5md.dll delivered with 2019Update2 but this did not change anything , and since the release notes for 2019Update3 did not mention any major modifications to OpenMP we did not try the 2019Update3 version of libiomp5md.dll. Surely a major fix like this is worth shouting about?

Regards

John Sturton

andrew_4619
Honored Contributor I
168 Views

cabrita, christophe wrote:
....and since the release notes for 2019Update3 did not mention any major modifications to OpenMP we did not try the 2019Update3 version of libiomp5md.dll. Surely a major fix like this is worth shouting about?

That is an issue that many users have complained about. You find a problem but get no visibility of when it is fixed. It used to be that if there was a thread discussing the problem the intel staff would at least add a note to it when that got fixed but even that does not happen any more and in fact intel only act on stuff that has a support ticket filed. Support issues have ZERO visibility for other users other than the person that files the ticket. An area of negative progress I am sorry to say. 

Reply