[Beowulf] very low performance for very small packets under MPICH (TCP_NODELAY?)
hahn at physics.mcmaster.ca
Fri Dec 30 11:11:35 PST 2005
> 2.6.15) with MPI 1.2.7 and Gigabit ethernet with a 3COM Switch and
> 3C2000-T NIC cards. We detected a very low efficiency in communication
which appears to use the sk98lin driver.
> packets or so times are in the order of 0.03~secs. This degrades the
> average performance for very small packets by a factor of 100.
is this measurable on real code, or only benchmarks? the reason I ask
is that real code probably doesn't generate a flood of tinygrams,
but the benchmark might, and if so would trigger interrupt mitigation.
> Any pointers for understanding why the Nagle algorithm is still active
why have you jumped to the conclusion that Nagle is at fault here?
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