[Beowulf] Nahalem / PCIe I/O write latency?

Larry Stewart stewart at serissa.com
Thu Oct 22 08:14:54 PDT 2009

Does anyone know, or know where to find out, how long it takes to do a store
to a device register on a Nahelem system with a PCIexpress device?  Also,
does write combining work with such a setup?

I recall that the QLogic Infinipath uses such features to get good short
message performance, but my memory of it is pre- Nahelem.

Question 2 - if the device stores to an address on which a core is spinning,
how long does it take for the core to return the new value?

These questions are to inform my thinking on PCIe device design.


(Apologies if a duplicate with misspellings appears, I sent an earlier
version from an off-list email.)
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