Overhead of using OpenMP?

[Tony_Garratt]

We build an application using v11 of your Fortran compiler which makes use of OpenMP. We run the exe with 1 thread and it takes around 6 mins. We re-compile and remove /QopenMP and re-run it and it takes around 6 mins. So, the use of OpenMP has a large overhead in the case when the code is run a single core machine. Is this expected?

Thanks!
Tony

[IanH]

You've got "6 mins" twice, which implies no overhead. Is this what you intended?

[Tony_Garratt]

Oh - sorry about that - here is what I meant to say:

We build an application using v11 of your Fortran compiler which makes use of OpenMP. We run the exe with 1 thread and it takes around9 mins. We re-compile and remove /QopenMP and re-run it and it takes around 6 mins. So, the use of OpenMP has a large overhead in the case when the code is run a single core machine. Is this expected?