Chapter 1. Hardware platforms for RHEL for Real Time

Caches have a noticeable impact on overall processing time and determinism. Often, the threads of an application need to synchronize access to a shared resource, such as a data structure.

With the tuna command line tool (CLI), you can determine the cache layout and bind interacting threads to a core so that they share the cache. Cache sharing reduces memory faults by ensuring that the mutual exclusion primitive (mutex, condition variables, or similar) and the data structure use the same cache.

Increasing the number of cores on systems can cause conflicting demands on the interconnects. This makes it necessary to determine the interconnect topology to help detect the conflicts that occur between the cores on real-time systems.

Many hardware vendors now provide a transparent network of interconnects between cores and memory, known as Non-uniform memory access (NUMA) architecture.

NUMA is a system memory design used in multiprocessing, where the memory access time depends on the memory location relative to the processor. When you use NUMA, a processor can access its own local memory faster than non-local memory, such as memory on another processor or memory shared between processors. On NUMA systems, understanding the interconnect topology helps to place threads that communicate frequently on adjacent cores.

The taskset and numactl utilities determine the CPU topology. taskset defines the CPU affinity without NUMA resources such as memory nodes and numactl controls the NUMA policy for processes and shared memory.