Ethernet communication from real time thread

["M. Koehrer" <mathias_koehrer@arcor.de>]

Hi all,

I have an application which is (so far) running using Xenomai and Rtnet.
I am about to evaluate this using the rt_preemption patch (V2.6.29.1-rt9).
It works quite smoothly, however I have some questions on the priorities that are used for
Ethernet, UDP/IP based network communication.
I have one separate NIC in my (Intel QuadCore) PC, that is used for a point-to-point connection
with an embedded device. Communication is done via UDP.
I have now a user thread (RT prio: 80) to do some computation and also the communication with
the embedded device. This thread is the only running on core 3.

My questions are now:
A call of send() in my user space application to transmit a UDP message 
ends up in the network stack of Linux.
Which real time priority will be used in the network stack?
Is it the priority of the user space thread that is calling send()?
Or is it the priority of the kernel thread [sirq-net-tx/3]?

On the receive side (calling recv()):
Which threads are relevant here?
IRQ-XX for the NIC's irq thread, [sirq-net-rx/3] or also the user space thread that is calling recv()?

Thanks for all feedback on that basic question!

Best regards

Mathias


-- 
Mathias Koehrer
mathias_koehrer@arcor.de


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