tracing: histogram internals doc, hist_debug, and misc

Hi Steve,

Here's the histogram internals documentation I promised awhile back
(second patch).

Accompanying it is a new config option that enables a new hist_debug
event file, which is used by the examples in the doc to display
some of the histogram internals (third patch).

The first patch is just a cleanup suggested by Masami that I
previously missed.

Thanks,

Tom

The following changes since commit 8e99cf91b99bb30e16727f10ad6828741c0e992f:

  tracing: Do not allocate buffer in trace_find_next_entry() in atomic (2020-04-03 11:30:50 -0400)

are available in the Git repository at:

  git://git.kernel.org/pub/scm/linux/kernel/git/zanussi/linux-trace.git ftrace/hist-design-doc-v1

Tom Zanussi (3):
  tracing: Check state.disabled in synth event trace functions
  tracing: Add histogram-design document
  tracing: Add hist_debug trace event files for histogram debugging

 Documentation/trace/histogram-design.rst | 2115 ++++++++++++++++++++++
 kernel/trace/Kconfig                     |   23 +
 kernel/trace/trace.h                     |    1 +
 kernel/trace/trace_events.c              |    4 +
 kernel/trace/trace_events_hist.c         |  292 ++-
 5 files changed, 2419 insertions(+), 16 deletions(-)
 create mode 100644 Documentation/trace/histogram-design.rst

-- 
2.17.1