I would say threading overhead as might be seen by an application. The tests in www.mcs.anl.gov/~thakur/thread-tests also try to measure that. I will point Sameer at those. Rajeev
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Pavan Balaji Sent: Wednesday, January 30, 2008 2:57 PM To: [email protected] Subject: Re: [mpich2-core] MPICH2 Threading Overhead
Yeah, I misunderstood the code. Darius pointed it out too. However, it again comes back to what exactly we want to measure -- threading overhead in MPICH2 or threading overhead in the overall communication and networking stack?
-- Pavan
On 01/30/2008 01:57 PM, Rajeev Thakur wrote:
Well the original code IBM sent does not have this 1 process limitation. See attached. The threads of a process communicate with the threads of another process. I think that is a better test. Why did we change it?
Rajeev
-----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Darius Buntinas Sent: Wednesday, January 30, 2008 1:07 PM To: [email protected] Subject: Re: [mpich2-core] MPICH2 Threading Overhead
I just want to check what the benchmark should do.
My understanding from the conference calls and Sameer's slides is that they're interested in the case where multiple threads of a process are sending/receiving to/from different processes. This allows the process to use multiple DMAs concurrently.
Right now, we've been testing the case where one process is sending/receiving with itself. So moving the locks around VCs may decrease the size of the CS, but will still serialize.
So what's the test we want to run?
I imagine something like P processes each with P-1 threads where each thread is communicating with a different process. But then we need a machine with P(P-1) cores.
On the 8-core nodes we have, we can run 3 processes with 2 threads each. But I think we need more threads to really stress things.
It seems that what we can see from the one or two processes is the just the effect of the size of the CS.
Comments?
-d
-- Pavan Balaji http://www.mcs.anl.gov/~balaji