[petsc-users] Recommended unknowns per processor

[TAY wee-beng]

On 3/8/2012 2:05 PM, Matthew Knepley wrote:
> On Fri, Aug 3, 2012 at 4:52 AM, TAY wee-beng <zonexo at gmail.com 
> <mailto:zonexo at gmail.com>> wrote:
>
>     On 3/8/2012 11:10 AM, thomas wrote:
>
>         Hi,
>         look at the FAQ
>
>         http://www.mcs.anl.gov/petsc/documentation/faq.html#slowerparallel
>
>         "There must be enough work for each process to overweigh the
>         communication time. We recommend an absolute minimum of about
>         10,000 unknowns per process, better is 20,000 or more."
>
>
>     Hi Thomas,
>
>     Thanks for the info.
>
>     Btw, is there an upper limit? When the unknowns are 100,000 or
>     more per process, is it better (as in faster) to use more
>     processes instead (e.g. 20,000 per process)?
>
>
> That depends on the machine. The lower limit is the minimum number of 
> unknowns to cover the latency of network communication.

Thanks for the info!
>
>    Matt
>
>
>         Regards
>         Thomas Huxhorn
>
>         On 08/03/2012 09:03 AM, TAY wee-beng wrote:
>
>             Hi,
>
>             I remembered that in one of the mails, someone mentions
>             the recommended
>             unknowns on each processor when doing parallel solving.
>
>             However, I can't find that mail. Can someone enlighten me?
>             Also, is this
>             number problem dependent?
>
>             Btw, I'm using PETSc to solve linear equations using BCGS.
>
>             Thanks!
>
>
>
>
>
>
> -- 
> What most experimenters take for granted before they begin their 
> experiments is infinitely more interesting than any results to which 
> their experiments lead.
> -- Norbert Wiener

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