You cannot look just at the VecAssemblyEnd() time, that will very likely give the wrong impression of the total time it takes to put the values in.
You need to register a new Event and put a PetscLogEvent() just before you start generating the vector entries and calling VecSetValues() and put the PetscLogEventEnd() just after the VecAssemblyEnd() this is the only way to get an accurate accounting of the time. Barry > On Jun 30, 2023, at 11:21 AM, Runfeng Jin <[email protected]> wrote: > > Hello! > > When I use PETSc build a sbaij matrix, I find a strange thing. When I > increase the number of processors, the assemble time become smaller. All > these are totally same matrix. The assemble time mainly arouse from message > passing, which because I use dynamic workload that it is random for which > elements are computed by which processor. > But from instinct, if use more processors, then more possible that the > processor computes elements storing in other processors. But from the output > of log_view, It seems when use more processors, the processors compute more > elements storing in its local(infer from that, with more processors, less > total amount of passed messages). > > What could cause this happened? Thank you! > > > Following is the output of log_view for 64\128\256 processors. Every row is > time profiler of VecAssemblyEnd. > > ------------------------------------------------------------------------------------------------------------------------ > processors Count Time (sec) > Flop > --- Global --- --- Stage ---- > Total > Max Ratio Max Ratio > Max Ratio Mess AvgLen Reduct > %T %F %M %L %R %T %F %M %L %R Mflop/s > 64 1 1.0 2.3775e+02 1.0 > 0.00e+00 0.0 6.2e+03 2.3e+04 9.0e+00 > 52 0 1 1 2 52 0 1 1 2 0 > 128 1 1.0 6.9945e+01 1.0 > 0.00e+00 0.0 2.5e+04 1.1e+04 9.0e+00 30 > 0 1 1 2 30 0 1 1 2 0 > 256 1 1.0 1.7445e+01 1.0 > 0.00e+00 0.0 9.9e+04 5.2e+03 9.0e+00 10 > 0 1 1 2 10 0 1 1 2 0 > > Runfeng Jin
