Hello, * On Oct,5 Roland Dreier<[EMAIL PROTECTED]> wrote : > Peter> If that is the purpose it fails badly since I have both > Peter> EM64T machines with PCI-X and AMD64 machines with > Peter> PCI-express. Or am I missing something here? > > Nope, the fact that it's messed up is what I was trying to point out. > >From a quick look at the code, it looks like you should set the > environment variable VIADEV_DEFAULT_MTU to "MTU1024" on PCI-X systems > and "MTU2048" on PCI Express systems. > > In general, one wants to use the largest possible MTU to get maximum > performance. However, Mellanox PCI-X HCAs have a quirk that causes an > MTU of 1024 to be faster than an MTU of 2048 for RC transport. This > quirk does not exist in PCI Express HCAs, and presumably PathScale and > IBM HCAs also perform best with the maximum possible MTU. So Mellanox > PCI-X HCAs are the only case where we want to use a lower MTU.
Since the MTU size can affect the performance and there are several different types of HCAs available in the market, we are working towards making a runtime decision of the MTU instead of compiling it in, or asking the user to input. This patch should be available sometime soon. Thanks, Sayantan. > > - R. > _______________________________________________ > openib-general mailing list > [email protected] > http://openib.org/mailman/listinfo/openib-general > > To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general -- http://www.cse.ohio-state.edu/~surs _______________________________________________ openib-general mailing list [email protected] http://openib.org/mailman/listinfo/openib-general To unsubscribe, please visit http://openib.org/mailman/listinfo/openib-general
