On Tue, May 01, 2012 at 10:27:42AM -0400, George Neville-Neil wrote:

The measurements are done with tools/tools/netrate/netsend and kernel patches to return from sendto() at various places in the stack (from the syscall entry point down to the device driver). A patch is attached.

You don't really need netmap to run it, it was just a convenient place to put the variables.

I am not sure how much we can "fix", there are multiple expensive functions on the tx path, and probably also on the rx path.

My hope at least for the tx path is that we can find out a way to install a "fastpath" handler in the socket. When there is no handler installed (e.g. on the first packet or unsupported protocols/interfaces) everything works as usual. Then when the packet reaches the bottom of the stack, we try to update the socket with a copy of the headers generated in the process, and the name of the fastpath function to be called. Next transmissions will then be able to shortcut the stack and go straight to the device output routine.

I don't have data on the receive path or good ideas on how to proceed -- the advantage of the tx path is that traffic is implicitly classified, whereas it might not be the case for incoming traffic, and classification might be the expensive step.

Hopefully we'll have time to discuss this next week in ottawa.