Messages in this thread |  | | Subject | RE: Problem with e100 driver and latency on different packet sizes | Date | Thu, 15 May 2003 10:12:34 -0700 | From | "Feldman, Scott" <> |
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> I've attached a small program to measure latency of > round-trip time on UDP. If I send 85-byte packets between > two of my machines, I get 170us round-trip latency. If I > send 86-byte packets, I get 1329us latency. > This seems quite odd. If I test on the eepro100 driver, I > get expected linear increase in round-trip time as the packet > size increases, and it never gets close to 1300us.
This sounds like a side-effect of the "CPU Cycle Saver" feature to bundle Rx packets per one interrupt. See Documentation/networking/e100.txt. I haven't tried your setup, but I would guess that you can play around with the BundleSmallFr module parameter, or better yet, if you want the lowest latencies, turn off CPU Saver (ucode=0).
CPU Saver trades latency for reduced interrupts, resulting in CPU savings, hence the name.
Hope this helps.
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