MPC85xx TSEC performance limits

MPC85xx TSEC performance limits

[Joyeau Sylvain]

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@825MHz :-(

Any idea how to get full TX bandwidth _without_ modifying this
parameter?

Thanks.

--
sylvain

Re: MPC85xx TSEC performance limits

[Pantelis Antoniou]

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@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.

Pantelis