Re: UDP/IP via Ethernet in real time (config-preempt patch)

[Stephen Hemminger]

On Tue, 17 Jul 2007 10:23:30 -0700
"Kok, Auke" <auke-jan.h.kok@xxxxxxxxx> wrote:

> M. Koehrer wrote:
> > Hi everybody,
> > 
> > I have a question concerning Ingo Molnar's realtime preempt patch.
> > This patch is great go get low latency on timer threads and a really
> > good real time behaviour.
> > I want to connect an external, embedded device via Ethernet (UDP/IP) 
> > to my Linux PC. This communication should be in real time as well.
> > For this I have a separate network adapter in my PC that is used
> > solely for this UDP Ethernet traffic.
> > However, I think all Ethernet traffic is be handled by
> > the soft IRQ threads [softirq-net-rx] [softirq-net-tx] but I do
> > not see a way to do real time networking via one of the network adapters.
> > 
> > How can I get this UDP networking real time capable?
> 
> In general, you'll have to find a non-NAPI ethernet driver and disable any form 
> of interrupt throttling. This will likely adversely affect throughput of course...
> 

RT kernel will also change the adapter hard irq into a work queue so it will
actually make the receive latency worse not better.
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