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CONFIG_OSNOISE_TRACER: OS Noise tracer

General informations

The Linux kernel configuration item CONFIG_OSNOISE_TRACER:

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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.

Hardware

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