I'll agree with Jeff that what you propose sounds right for avg. round-trip time.
Just thought I'd mention that when people talk about the ping-pong latency or MPI latency benchmarks, they are usually referring to 1/2 the round-trip time. So you compute everything the same as you did, and then divide by 2. But if your professor clearly said round-trip, I'd agree that you need to get a clearer definition of what he's looking for. Maybe it's units. If he asked for round-trip time in microseconds, you have to adjust your formula. -Tom > -----Original Message----- > From: users-boun...@open-mpi.org [mailto:users-boun...@open-mpi.org] On > Behalf Of Jeff Squyres > Sent: Tuesday, October 09, 2012 2:58 AM > To: Open MPI Users > Subject: Re: [OMPI users] Communication Round-trip time > > In general, what you said is "right"... for some definition of "right". :-) > > Usually, benchmarking programs start a timer, do the round trip sends N times, > stop the timer, and then divide the total time by N (to get a smoother > definition > of "average"). > > But keep in mind that there are many, many factors involved here. For > example, > it is also common to do "warmup" round trip communications -- do, say, 100 > round-trip communications before you start the timer. This allows MPI to > establish connections and do any other startup processing that isn't a factor > during steady-state communications. > > More specifically, the definitions of "right" and "wrong" very much depend on > what is in your professor's head. Every benchmark is different; there are > many > similar-but-slightly-different benchmark definitions out there. You'll need > to > figure out exactly what he is looking for; sorry. > > > > On Oct 8, 2012, at 10:59 PM, huydanlin wrote: > > > I'm currently doing MPI project in NUS University. My professor require > > me > make a monitoring tool to check the connection among processes in Cluster. > And also measure communication round-trip time. > > My solution is : > > 1. At the source process : start MPI_Send > > 2. At the destination process : start MPI_Recv to receive the message from > source > > 3. At the destination process : start MPI_Send to send immediately the same > message to source > > 4. At the source process : start MPI_Recv to receive the message from > destination > > I start timer( before (1) - t1=MPI_Wtime & after (4) - t2=MPI_Wtime ) > > then t2 - t1 is time for communication. I also do (1) to (4) for N > > times. then i > calculate the avg round-trip time by (t2-t1)/N. > > So is it right? Because he tells it 's wrong. And what exactly is the > communication round-trip time ? > > Regards and hope to see your reply soon. > > _______________________________________________ > > users mailing list > > us...@open-mpi.org > > http://www.open-mpi.org/mailman/listinfo.cgi/users > > > -- > Jeff Squyres > jsquy...@cisco.com > For corporate legal information go to: > http://www.cisco.com/web/about/doing_business/legal/cri/ > > > _______________________________________________ > users mailing list > us...@open-mpi.org > http://www.open-mpi.org/mailman/listinfo.cgi/users
