MPC85xx TSEC performance limits

Joyeau Sylvain Sylvain.Joyeau at
Wed Mar 1 23:23:49 EST 2006


Does anybody already succeeded in getting full TX bandwidth on a TSEC
interface, transmitting 1500 bytes frames at netdev level (ie calling
directly dev_queue_xmit(skb)) for instance ?

With default Gianfar driver parameters, I can transmit only around
870Mb/s (while reception side is idle). The other TSEC interface is used
only to control a telnet terminal (~1Kb/s), the CPU is idle 60%,

I must decrease TX threshold value from 1024 to 128 to get 960Mb/s.

The problem is that decreasing the TX threshold under 512 bytes has a
dramatic side effect: the Gianfar driver generates "TX underrun" events
as soon as  I start, in parallel, a DMA transfer from memory to memory.
Rather disappointing behavior from a PQ3 at 825MHz :-(

Any idea how to get full TX bandwidth _without_ modifying this



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