latency doubled on tg3 device from 2.6.11 to 2.6.12

Rick Warner
2005-09-01T21:32:11Z

Hello,
We have been testing latency and bandwidth using our proprietary MPI link
checker tool (http://www.microway.com/mpilinkchecker.html) and have found
that the latency increased from ~25ms to ~45ms going from 2.6.11 to 2.6.12.
2.6.13 has the same result. We also tried the latest bcm5700 from broadcom
(8.2.18) and got the same ~45ms latencies. This was tried on several
different opteron and em64t motherboards.

We see 20-25ms latencies with the e1000 driver (with some module options) on
all 3 kernel versions. For those interested, the e1000 options used are:

InterruptThrottleRate=0 RxIntDelay=0 TxIntDelay=0 RxAbsIntDelay=0
TxAbsIntDelay=0

Digging through source, it seems that a new locking mechanism for tg3 was put
in place in 2.6.12. Is this the likely cause? What can we do to restore our
lower latency?

--
Richard Warner
Lead Systems Integrator
Microway, Inc
(508)732-5517