Tracer to detect hardware latencies (like SMIs)

modulename: trace_hwlat.ko


Linux Kernel Configuration
└─>Kernel hacking
└─>Tracer to detect hardware latencies (like SMIs)
In linux kernel since version 3.10 (release Date: 2013-06-30)  
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

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.

source code: