Molcas Forum

vkj

Member

Registered: 2019-04-10

Posts: 31

OpenMP doesnt work in latest master branch

Dear developers,

Compiling OpenMolcas with openmp (-DOPENMP=ON) doesn't seem to work. If i launch the a molcas calculation with OMP_NUM_THREADS and MKL_NUM_THREADS > 1, the output still says its using only 1 thread.  I have older installations where OpenMP multiple threads worked in both SERIAL and MPI parallelized versions.

I confirmed that i switch to an older tag/v22.06 and compile in exactly the same environment and launch the same calculation I can see multiple threads running as reported in molcas output.

vkj

Ignacio

Administrator

From: Uppsala

Registered: 2015-11-03

Posts: 1,194

Re: OpenMP doesnt work in latest master branch

Try with MOLCAS_THREADS=X or "pymolcas -nt X"

vkj

Member

Registered: 2019-04-10

Posts: 31

Re: OpenMP doesnt work in latest master branch

I confirm that the MOLCAS_THREADS option WORKS. I can see multiple threads being used as reflected in output and also processor usage monitored with top.

Unfortunately, atleast for my system/setup I cant see any advantages of OMP/MKL multiple threads speedups.

Calculation Information:                         
Number of basis functions: 444

RICD=ACTIVE

&RASSCF
Symm=1
charge=0
ras1=5
ras2=0
ras3=5
nactel=10 4 4
CIRoot=6 6 1
NOQUNE
THRS=1.0D-08 1.0D-02 1.0D-02

CIROOT=6 6 1

&CASPT2
xmultistate=ALL
IMAG = 0.2
IPEA = 0.0

System Information
2 X Intel(R) Xeon(R) CPU E5-2640 v4 @ 2.40GHz
Memory = 236 GB

Compilation
GCC - 7.3.1
Linear Algebra - MKL from parallelstudio2019 ; Openblas 0.2.20

Timings are given for SEWARD/RASSCF/CASPT2 in the format of :MINUTES/:MINUTES/HOURS:MINUTES

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                 SERIAL          NPROCS=2;THREADS=1   NPROCS=4;THREADS=1   NPROCS=1;THREADS=2   NPROCS=1;THREADS=4 
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  Internal                  :11/:24/07:45             :10/:13/04:58                      :08/:07/03:29                                               
  OpenBLAS            :03/:15/02:54             :03/:11/02:23                      :02/:07/02:12                        :03/:20/04:51                           :03/:16/04:28     
    MKL                      :02/:14/02:50            :02/:10/02:07                      :01/:06/02:08                        :02/:18/03:29                           :02/:18/03:44     
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Its puzzling that the timings for Openmolcas_v22.06 are different when enabling multiple threads. I dont see speedups but also not so much slowdowns. I checked with ldd the various .exe are linked to proper libraries.

--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
                                NPROCS=1;THREADS=4 
---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

  OpenBLAS                            :03/:18/02:37     
    MKL                                     :01/:17/02:35     
----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Last edited by vkj (2024-05-15 08:06:40)