Thanks for your answer.I only run one job only. do not
run others.
If I said there is posible two processors run slower
than one processor because one become master and just
send the data and recv data only and another one is
just recv data and do calculation,then send back to
master. No parallel processing happen here.
I assume that the adition time is for sending and
recving data. Am I right?
p/s:compare with distributed memory, generally, witch
one is more faster? thanks.
--- Xuehua Chen <cxh_at_[hidden]> wrote:
> Hi, this is funny. How can two processors run slower
> than one processor? Are there other jobs running?
> Does it has intensive computation or memory access.
> I doubt there are many memory accesses in the code.
> For shared memory, two processors trying to access
> memory at the same time cause contention. Also,
> it could happen that here one process utilize
> cache much better the one processor. I think
> it's hard to tell which factor cause the problem
> unless you test time spend on different functions.
>
> I think it's very probable that when your program
> run the
> on two processors, some other jobs that use cpu or
> memory are running. Have you tried run both cases
> multiple times with all other jobs idle?
>
> Hehe, Very interested in the result you get and
> hope to get more info from you.
>
> Xuehua Chen
> On Wed, 2003-04-09 at 22:31, choy hau yan wrote:
> > I use 2 processor for parallel in shared memory.
> >
> > When I run in one processor (no parallel) the time
> of
> > calculation is 5157 seconds.
> >
> > when run in 2 processor,(one master, one slave)
> the
> > time is 5324 seconds.
> > So, the time communications is 167 seconds. As I
> know
> > there is nearly no communication in shared memory.
> So
> > what is the reason that contribute the time (167
> > seconds.) Thanks.
> >
> > p/s.I just use mpi_send and mpi_recv.
> >
> > __________________________________________________
> > Do you Yahoo!?
> > Yahoo! Tax Center - File online, calculators,
> forms, and more
> > http://tax.yahoo.com
> > _______________________________________________
> > This list is archived at
> http://www.lam-mpi.org/MailArchives/lam/
> >
> >
>
>
>
> _______________________________________________
> This list is archived at
http://www.lam-mpi.org/MailArchives/lam/
__________________________________________________
Do you Yahoo!?
Yahoo! Tax Center - File online, calculators, forms, and more
http://tax.yahoo.com
|
