On Mon, 7 Jul 2008, Bruce Evans wrote:
I use low-end memory, but on the machine that does 640 kpps it somehow has
latency almost 4 times as low as on new FreeBSD cluster machines (~42 nsec
instead of ~150). perfmon (fixed for AXP and A64) and hwpmc report an
average of 11 k8-dc-misses per sendto() while sending via bge at 640 kpps.
11 * 42 accounts for 442 nsec out of the 1562 per packet at this rate. 11 *
150 = 1650 would probably make this rate unachievable despite the system
having 20 times as much CPU and bus.
Since you're doing fine-grained performance measurements of a code path that
interests me a lot, could you compare the cost per-send on UDP for the
following four cases:
(1) sendto() to a specific address and port on a socket that has been bound to
INADDR_ANY and a specific port.
(2) sendto() on a specific address and port on a socket that has been bound to
a specific IP address (not INADDR_ANY) and a specific port.
(3) send() on a socket that has been connect()'d to a specific IP address and
a specific port, and bound to INADDR_ANY and a specific port.
(4) send() on a socket that has been connect()'d to a specific IP address
and a specific port, and bound to a specific IP address (not INADDR_ANY)
and a specific port.
The last of these should really be quite a bit faster than the first of these,
but I'd be interested in seeing specific measurements for each if that's
possible!
Thanks,
Robert N M Watson
Computer Laboratory
University of Cambridge
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