verifying SMP

[Joachim Worringen]

Gabriel J. Weinstock:
> Hi,
>   Does anyone know a good way to test if a certain process is running on
> different CPUs on an SMP cluster node? For example, if one were to mpirun
> -np 4 prog where the machines file looked like
> node1:2
> node2:2
>   how could you verify that one process is being started on each CPU? Using
> top is one option, but then you're still inferring where the process is
> running. We're seeing funny numbers in our code and would like to verify
> where Linux is scheduling processes.

>From my experience, this ("processor affinity of processes") is not (yet?) 
available in Linux. The effects you have (which ones exactly?) are probably 
cache effects in cases that a process is running on CPU X for one timeslot, 
and running on CPU Y for the next timeslot (loosing the cache contents of CPU 
X).

The Win32 API (sic!), and i.e. Solaris, have nice functions (see 
http://www.sybase.com/detail/1,6904,1010600,00.html) to do this, and this 
improves performances for certain scenarios (esp. 1:1 mapping of CPU-hungry 
processes). There's still much left to improve in the Linux kernel... 

 Joachim

-- 
Joachim Worringen - NEC C&C research lab St.Augustin
fon +49-2241-9252.20 - fax .99 - http://www.ccrl-nece.de

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