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CONFIG_HWLAT_TRACER: Tracer to detect hardware latencies (like SMIs)

General informations

The Linux kernel configuration item CONFIG_HWLAT_TRACER:

Help text

This tracer, when enabled will create one or more kernel threads, depending on what the cpumask file is set to, which each thread spinning in a loop looking for interruptions caused by something other than the kernel. For example, if a System Management Interrupt (SMI) takes a noticeable amount of time, this tracer will detect it. This is useful for testing if a system is reliable for Real Time tasks.

Some files are created in the tracing directory when this is enabled:

hwlat_detector/width - time in usecs for how long to spin for hwlat_detector/window - time in usecs between the start of each iteration

A kernel thread is created that will spin with interrupts disabled for "width" microseconds in every "window" cycle. It will not spin for "window - width" microseconds, where the system can continue to operate.

The output will appear in the trace and trace_pipe files.

When the tracer is not running, it has no affect on the system, but when it is running, it can cause the system to be periodically non responsive. Do not run this tracer on a production system.

To enable this tracer, echo in "hwlat" into the current_tracer file. Every time a latency is greater than tracing_thresh, it will be recorded into the ring buffer.



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