On Mon, 11 Jun 2007, Kip Macy wrote:
I think its a windowism, stands for Receive Side Scaling, and what it means
is multiple receive queues, each with an MSI/X vector so they can interrupt
different CPUs, or they can be tied to virtual guests, or MACs, etc etc...
AFAICT FreeBSD can't currently benefit from this as there is no cpu affinity
for connections. I may be wrong, but I see lower single-connection
throughput using a receive queue per core than using a single receive queue.
RSS is done by hashing a TCP tuple (I'm deliberately vague because at least
with cxgb there are multiple combinations, the default is the standard
4-tuple) to a receive queue.
If you're looking at concurrent TCP input processing, the tcbinfo lock is
likely one source of overhead due to high contention. I had hoped to make
further progress on this for 7.0 (it's already better than 6.0 in a number of
ways), but the instability of 7.x over the last month scuttled that project.
It will have to be an 8.0 thing, but perhaps we can look at an MFC if that
goes well. I have some initial protyping but have been waiting for TCP to
settle down again a bit before really digging in.
Robert N M Watson
Computer Laboratory
University of Cambridge
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