[petsc-users] Understanding PETSc -log_summary

[Barry Smith]

  Also this information at the top is often not particularly useful because it includes start up time and any IO etc.

  We recommend looking that the events below. You can start with the line for TSSolve, or SNESSolve, or KSPSolve depending on if you are using TS, SNES, or KSP. There are similar "load balance" information in each row.

   Barry

> On Mar 16, 2017, at 10:11 AM, Ajit Desai <aero.aju at gmail.com> wrote:
> 
> Thanks, Jed.
> That is helpful. 
> 
> Ajit Desai
>  PhD Scholar, Carleton University, Canada
> 
> On Thu, Mar 16, 2017 at 8:00 AM, Jed Brown <jed at jedbrown.org> wrote:
> Ajit Desai <aero.aju at gmail.com> writes:
> 
> > Hello Everyone,
> > A couple of questions on the *-log_summary* provided by PETSc.
> 
> -log_view is the preferred name.
> 
> > 1. *Avg-Flops & Avg-Flops/sec* are averaged among the participating cores
> > or averaged over the simulation time or both?
> 
> Flops on each process is just the count (as logged by PetscLogFlops,
> which PETSc numerical functions call and you can too) over the time
> between PetscInitialize until the log is printed (usually
> PetscFinalize).  The time on each process is the wall clock time from
> PetscInitialize until the log is printed.  The Average, Max, Min, and
> total are over processes.
> 
> > 2. *Max/Min Flops & Flops/sec* is an indication of load balancing?
> > In simulation-2 these ratios are high compared to simulation-1. Does that
> > mean simulation-2 is not well balanced?
> 
> Yes, not balanced in terms of flops (correlated with time, but not a
> measure of time).  Look at the events to help see where.
> 
> > Please follow the outputs from two different simulations
> > (Note: the problem size and the number of processors used are different).
> >
> > *Simulation-1*
> >                                    Max           Max/Min        Avg
> >    Total
> > Time (sec):            4.208e+02      1.00005   4.208e+02
> > Objects:                 7.100e+01      1.00000   7.100e+01
> > Flops:                     3.326e+11      1.31175   3.017e+11  4.826e+13
> > Flops/sec:              7.904e+08      1.31175   7.169e+08  1.147e+11
> > MPI Messages:      0.000e+00      0.00000   0.000e+00  0.000e+00
> >
> >
> > *SImulation-2:*
> >                                   Max          Max/Min        Avg
> > Total
> > Time (sec):           8.434e+02      1.00000   8.434e+02
> > Objects:                7.300e+01      1.02817   7.102e+01
> > Flops:                   6.555e+11      1.85115   5.798e+11  3.711e+14
> > Flops/sec:            7.772e+08      1.85115   6.874e+08  4.400e+11
> > MPI Messages:    0.000e+00      0.00000   0.000e+00  0.000e+00
> >
> > We're trying to understand the performance of our solver using these
> > outputs.
> > Any comments in relation to that will be helpful.
> >
> > Thanks & Regards,
> > *Ajit Desai*
> >  PhD Scholar, Carleton University, Canada
>