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Subject: Re: [OMPI users] Regarding the execution time calculation
From: Jeff Squyres (jsquyres_at_[hidden])
Date: 2012-05-04 08:05:22


A few nodes:

1. I think you posted an incorrect version of your code -- it's calling MPI_Test on an uninitialized request.

2. This looks like a homework problem. I try very hard not to do peoples' homework. :-) My first comment to you stands: you need to be more fine-grained in your timing and figure out where the increase in time is coming from. Here's another hint: compare the relative sizes of execution times of the different parts of your program and use that to deduce why your program is not scaling.

Good luck!

On May 4, 2012, at 7:44 AM, seshendra seshu wrote:

> Hi,
> I haven't used the more mpi process also but still am still unable to reduce my exection time.Here is my code http://seshendramln.blogspot.se/
> and please help me in solving.
> In this code iam getting the same execution time in i increase or decrease the no.of nodes.
>
> thanking you
>
>
> With regards
> seshendra
>
>
> On Fri, May 4, 2012 at 12:55 PM, Jeff Squyres <jsquyres_at_[hidden]> wrote:
> You probably need to be more fine-grained in your timing. Find out exactly what is increasing in time. This is a common symptom for codes that do not scale well -- i.e., adding more MPI processes actually causes it to slow down.
>
>
> On May 3, 2012, at 7:48 AM, seshendra seshu wrote:
>
> > Hi,
> > I have written an parallel program and when i run my program on 4,8,16 nodes and calculated the execution time at master using MPI_Wtime in master node. The problem the execution time is increasing rapidly like NON parallel program-55 sec, and for parallel program 2-nodes--60sec , 4-nodes 74sec, 8-node--120 sec and for 16 nodes---for 180 sec. can i know my problem in parallel version actually the time needs to be decreased but it is increasing i dont the reason. i have calculated my time as shown below
> >
> >
> > main(argv,argc)
> > {
> > double start,end;
> > start= MPI_Wtime;
> > // done some work
> > {
> > // start send from master node and receiving it
> > end =MPI_Wtime;
> > cout<<"execution time"<<end-start;
> > }
> > //in slave nodes done some work
> > MPI_Finalize;
> > }
> >
> > Please help me in solving this problem.
> >
> > --
> > WITH REGARDS
> > M.L.N.Seshendra
> > _______________________________________________
> > users mailing list
> > users_at_[hidden]
> > http://www.open-mpi.org/mailman/listinfo.cgi/users
>
>
> --
> Jeff Squyres
> jsquyres_at_[hidden]
> For corporate legal information go to: http://www.cisco.com/web/about/doing_business/legal/cri/
>
>
> _______________________________________________
> users mailing list
> users_at_[hidden]
> http://www.open-mpi.org/mailman/listinfo.cgi/users
>
>
>
> --
> WITH REGARDS
> M.L.N.Seshendra
> _______________________________________________
> users mailing list
> users_at_[hidden]
> http://www.open-mpi.org/mailman/listinfo.cgi/users

-- 
Jeff Squyres
jsquyres_at_[hidden]
For corporate legal information go to: http://www.cisco.com/web/about/doing_business/legal/cri/