latency doubled on tg3 device from 2.6.11 to 2.6.12

[Rick Warner]

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
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