[gmx-developers] MPI_sendrecv and specific timing

[David]

On Wed, 2005-07-13 at 14:33 -0500, Nathan Moore wrote:
> Fellows,
> 
> So I've included the revised version of move_f and move_x from the old
> source revision (1.8) of mvxvf.c.  I notice a slight speedup in the dpcc
> benchmark, but signifigant time remains in the MPI Sendrecv command -
> (about 10% of execution wall time).  The only other place in the source I
> can find MPI_Sendrecv is in stat.c's moveit function, used via #define
> with the MX( macro.
> 
> Should moveit really be eating up 10% of execution?
No, if you put a MPI_Barrier straight before it, you will see that the
time is in MPI_Barrier instead, ergo it is load unbalance.
> 
> regards,
> 
> Nathan Moore
> 
> timing, dpcc, 5000 timesteps, np=64, in seconds, median processor
> statistics below:
> 
> version 3.2
> 
> MPI Routine                  #calls     avg. bytes      time(sec)
> -----------------------------------------------------------------
> MPI_Comm_size                     1            0.0          0.000
> MPI_Comm_rank                     1            0.0          0.000
> MPI_Send                        749        27628.6          0.214
> MPI_Isend                    693883        32055.4          1.240
> MPI_Recv                        749        27628.6         23.499
> MPI_Irecv                    693883        32055.4          0.562
> MPI_Sendrecv                 320190        45696.0        195.866
> MPI_Wait                    2028146            0.0        238.088
> 
> v 3.2 with collective move_f and move_x
> 
> MPI Routine                  #calls     avg. bytes      time(sec)
> -----------------------------------------------------------------
> MPI_Comm_size                     1            0.0          0.000
> MPI_Comm_rank                     1            0.0          0.000
> MPI_Send                        749        27628.6          0.218
> MPI_Isend                    693883        32055.4          1.301
> MPI_Recv                        749        27628.6         14.872
> MPI_Irecv                    693883        32055.4          0.484
> MPI_Sendrecv                 160158        45696.0        108.985
> MPI_Wait                    1708082            0.0        245.779
> MPI_Allgatherv                 5001        45696.0         68.676
> 
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-- 
David.
________________________________________________________________________
David van der Spoel, PhD, Assoc. Prof., Molecular Biophysics group,
Dept. of Cell and Molecular Biology, Uppsala University.
Husargatan 3, Box 596,          75124 Uppsala, Sweden
phone:  46 18 471 4205          fax: 46 18 511 755
spoel at xray.bmc.uu.se    spoel at gromacs.org   http://xray.bmc.uu.se/~spoel
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