[petsc-users] Software for load balancing to improve parallel performance to be used with PETSc

[Jed Brown]

On Thu, Jan 5, 2012 at 09:41, TAY wee-beng <zonexo at gmail.com> wrote:

> I just did a -log_summary and attach the text file, running across 8 and
> 16 processors. My most important concern is whether the load is balanced
> across the processors.
>
> In 16 processors case, for the time, it seems that the ratio for many
> events are higher than 1, reaching up to 6.8 for VecScatterEnd
>

This takes about 1% of the run time and it's scaling well, so don't worry
about it.


> and 132.1 (?) for MatAssemblyBegin.
>

This is about 2% of run time, but it's not scaling. Do you compute a lot of
matrix entries on processes that don't own the rows?

Most of your solve time is going into PCSetUp() and PCApply, both of which
are getting more expensive as you add processes. These are more than 10x
more than spent in MatMult() and MatMult() takes slightly less time on more
processes, so the increase isn't entirely due to memory issues.

What methods are you using?


> However, for the flops, ratios are 1 and 1.1. so which is more important
> to look at? time or flops?
>

If you would rather do a lot of flops than solve the problem in a
reasonable amount of time, you might as well use dense methods. ;-)
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