Thomas Gleixner and Sebastian Siewior, Linutronix GmbH, Germany

Even if the latest PREEMPT_RT patched Linux kernel is used, the network stack can inflict unbound latencies on real-time Ethernet protocols due to:

• Socket buffer allocations
  
• Traffic congestion with non real-time traffic

In a proof-of-concept implementation, the following mechanisms are used
to overcome the above limitations:

• Generic preallocated socket buffer pools
• Protocol-specific traffic policing and traffic shaping

This approach is minimally invasive to the network stack and has zero impact when the real-time protocol related functions are not enabled:

• Network card drivers require no or minimal changes to support preallocated buffer pools
• Traffic control is modular and only loaded and enabled when required
• No restriction on network tools and network functionality

The paper does not cover the complex user space part of real-time Ethernet protocols.