From owner-freebsd-net@FreeBSD.ORG  Mon Jun 27 16:52:49 2011
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Date: Mon, 27 Jun 2011 19:09:25 +0200
From: Luigi Rizzo <rizzo@iet.unipi.it>
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Subject: RTL8169 (if_re) poor tx packet rate ?
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Asking just in case someone has experience on the sending rate
with Realtek 8168/8169/8110 Gbit cards.

On the receive side, using netmap, even with the CPU at 200 MHz the
card seems able to receive 1.38 Mpps (the most i can generate with
my other, intel 1 Gbit/s cards).

But on the receive side the most i get is 370 Kpps (with 64-byte
packets), and achieve slightly faster speeds (390Kpps) only sending
shorter frames (16 bytes) and relying on the padding inserted by
the card. Even the standard drivers reach similar speeds
(in the 300Kpps range).

I have tried to change several configuration parameters in
the NIC settings (tx dma threshold, mitigation, checked
the inter-packet gap, increasing the ring size to 1024) but they
seem to have no effect.

The only improvement (but a very modest one) is if i use the "high
priority" tx ring instead of the regular one -- then speed goes up
from 365 to 370 Kpps (very reproducible).

At much larger packet sizes (1024 and above) the card does line rate
with no problems.

Has anyone tried to push these cards at high speed, or do you have
suggestions on what to try ?

cheers
luigi

http://info.iet.unipi.it/~luigi/netmap/