tree 85e0a89d3ffdc74ff335ff53f42f3f05b0d2da41
parent 75a3b99d0f57910eeb24f3cfbbc6337d0f236d17
author Steven Rostedt (Red Hat) <rostedt@goodmis.org> 1428500004 -0400
committer Steven Rostedt <rostedt@goodmis.org> 1429645168 -0400

tracing: Add hwlat_detector tracer

Connect the hwlat_detector written by Jon Masters with the
tracing system as a new ftrace tracer.

A few files are created when the hwlat_detector is enabled
that exist in the tracing directory.

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

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

To enable the tracer, simple echo in "hwlat_detector" into
"current_tracer"

 # echo hwlat_detector > /sys/kernel/debug/tracing/current_tracer

Every time a hardware latency is found that is greater than
tracing_thresh (set and viewed by the tracing_thresh file in the
tracing directory), it is reported into the ftrace ring buffer.

The default value of tracing_thresh (if it was zero when the
hwlat_detector tracer began) is 10us. If it is not zero, the
threshold does not change.

The max latency found is set in the tracing_max_latency file.

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>