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.
>
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