MPC85xx TSEC performance limits

Pantelis Antoniou pantelis at
Thu Mar 2 02:25:40 EST 2006

On Wednesday 01 March 2006 14:23, Joyeau Sylvain wrote:
> Hi,
> 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%,
> 6000irq/s.
> 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
> parameter?
> Thanks.
> --
> sylvain

I don't know 85xx in any great detail, but most QUICCs have a register
that controls the DMA bus arbitration priorities. Find it and give
the highest priority to the ethernet.


More information about the Linuxppc-embedded mailing list