Update karolina-compilation.md

docs.it4i/software/karolina-compilation.md

@@ -40,9 +40,12 @@ OMP_NUM_THREADS = 64
 GOMP_CPU_AFFINITY=0:63:1
 ```
 
-However, to get full performance, you have to execute two jobs on the two Karolina sockets at the time.
+However, to get full performance, you have to execute two jobs on two Karolina sockets at the time.
 Other BLAS libraries may be used, however none performs as well as the MKL.
 
+!!! note
+    Most MPI libraries do the binding automatically. The binding of MPI ranks can be inspected for any MPI by running `$ mpirun -n num_of_ranks numactl --show`. However, If the ranks spawn threads, binding of these threads should be done via the environment variables described above.
+
 The choice of BLAS library and its performance may be verified with our benchmark,
 see [Lorenz BLAS performance benchmark][a].