In the context of high-performance computing (HPC), the Operating
System Noise (osnoise) refers to the interference experienced by an
application due to activities inside the operating system. In the
context of Linux, NMIs, IRQs, SoftIRQs, and any other system thread
can cause noise to the system. Moreover, hardware-related jobs can
also cause noise, for example, via SMIs.

The osnoise tracer leverages the hwlat_detector by running a similar
loop with preemption, SoftIRQs and IRQs enabled, thus allowing all
the sources of osnoise during its execution. The osnoise tracer takes
note of the entry and exit point of any source of interferences,
increasing a per-cpu interference counter. It saves an interference
counter for each source of interference. The interference counter for
NMI, IRQs, SoftIRQs, and threads is increased anytime the tool
observes these interferences' entry events. When a noise happens
without any interference from the operating system level, the
hardware noise counter increases, pointing to a hardware-related
noise. In this way, osnoise can account for any source of
interference. At the end of the period, the osnoise tracer prints
the sum of all noise, the max single noise, the percentage of CPU
available for the thread, and the counters for the noise sources.

In addition to the tracer, a set of tracepoints were added to
facilitate the identification of the osnoise source.

The output will appear in the trace and trace_pipe files.

To enable this tracer, echo in "osnoise" into the current_tracer
file.

source code:

kernel/trace/trace_osnoise.c