What do you mean by logical partition? For 2 partitions it a single slice and for 4 partitions it is a plus shape slice partitioning. The computation is decreasing continuously but communication time is increasing from 0.69% to 8.9% of the total time from 2 to 4 processes. I am using MPI_Neighbor_alltoallw for exchanging data after forming distributed graph topology. On Fri, May 8, 2020 at 8:34 PM Zhou, Hui <[email protected]> wrote:

I would first analyze the logical partition and the effects on computation and communications. Do they continuously change from 2 process and up or is there a bump?

-- Hui Zhou

*From: *hritikesh semwal via discuss <[email protected]> *Reply-To: *"[email protected]" <[email protected]> *Date: *Thursday, May 7, 2020 at 11:19 PM *To: *"[email protected]" <[email protected]> *Cc: *hritikesh semwal <[email protected]> *Subject: *[mpich-discuss] Speed up issue with CFD solver.

Hello,

I am developing a parallel CFD solver for unstructured grids with finite volume explicit time integration method and the global mesh count is 97336 cells. I am trying to get the speed up results of my code but something strange is happening. Following are my timing results after the second time step with the different number of processors;

2 processors- 182.284 seconds

4 processors- 251.7035 seconds

8 processors- 190.8578 seconds

16 processors- 129.7989 seconds

24 processors- 121.0303 seconds

32 processors- 111.3772 seconds

I am not getting why there is a sharp rise in time from 2 processors to 4 processors and after that, it is decreasing. I had run the same code 2 weeks ago and at that time the results were different from the present results and time was continuously decreasing at that time. Could someone please help me with this matter by suggesting the probable cause/s of this behaviour?

Thank you.