Ingo,

What follows is a set of three patches against tip/master that
implement a 'latency' sub-command for perf. You can also get it
by fetching the perf-latency-master branch from:

git://git.kernel.org/pub/scm/linux/kernel/git/clrkwllms/rt-linux.git

The 'perf latency' command is an interface for managing the 
hwlat_detector kernel module via its debufs interface. The kernel 
module polls the TSC looking for gaps and when a gap exceeding a
specified threshold is detected, a timestamp and the gap value (in
microseconds) is printed to stdout.

The command line arguments are a sample interval (--window), sample
duration within that window (--width), a duration for the length of
time the test should run (--duration) and a threshold (--threshold)
above which is considered a hardware latency. 

Clark Williams (3):
  debugfs utility routines for perf
  modify perf routines to use new debugfs routines
  perf latency builtin command

 tools/perf/Documentation/perf-latency.txt |   64 +++++
 tools/perf/Documentation/perf.txt         |    2 +-
 tools/perf/Makefile                       |    3 +
 tools/perf/builtin-latency.c              |  383
 +++++++++++++++++++++++++++++
 tools/perf/builtin.h                      |    2 +-
 tools/perf/command-list.txt               |    1 +
 tools/perf/perf.c                         |   45 +---
 tools/perf/util/debugfs.c                 |  241 ++++++++++++++++++
 tools/perf/util/debugfs.h                 |   22 ++
 tools/perf/util/parse-events.c            |   17 +- 10 files changed,
 727 insertions(+), 53 deletions(-) create mode 100644
 tools/perf/Documentation/perf-latency.txt create mode 100644
 tools/perf/builtin-latency.c create mode 100644
 tools/perf/util/debugfs.c create mode 100644 tools/perf/util/debugfs.h