[PATCH v7 00/10] tracing: 'hist' triggers

[Tom Zanussi]

This is v7 of the 'hist triggers' patchset, following feedback from
v6.

Changes from v6:

This version adds a new 'sym-offset' modifier as requested by Masami.
I implemented it as a modifier rather than using the trace option as
suggested, in part because I wanted to keep it all self-contained and
it seemed more consistent to just add it alongside the 'sym' modifier.
Also, hist triggers arent't really a tracer and therefore don't
directly tie into the option update/callback mechanism so making use
of it isn't as simple as a normal tracer.

I also changed the sort key specification to be stricter and signal an
error if the specified sort key wasn't found (rather than defaulting
to hitcount in those cases), also suggested by Masami.  Thanks,
Masami, for your input!

Also updated the Documentation and tracing/README to reflect the
changes.

Changes from v5:

This version adds support for compound keys, along with the related
ability to sort using primary and secondary keys.  This was mentioned
in previous versions as the last important piece that remained
unimplemented, and is now implemented.  (I didn't have time to get to
the couple of enhancements suggested by Masami, but I expect to be
able to add those later on top of these.)

Because we now support compound keys and it's not immediately clear in
the output exactly which fields correspond to keys, the key(s),
compound or not, are now enclosed by curly braces.

The Documentation and README have been updated to reflect the changes,
and several new examples have been added to illustrate how to use
compound keys.

Also, the code was updated to work with the new ftrace_event_file,
etc, renaming in tracing/for-next.

Changes from v4:

This version addresses some problems and suggestions made by Daniel
Wagner - a lot of the code was reworked to get rid of the distinction
between keys and values, and as a result, both keys and values can be
used as sort keys.  As suggested, it also allows 'val=' to be absent
in a trigger command - if no 'val' is specified, hitcount is assumed
and automatically used as the only val.

The map code was also separated out into a separate file,
tracing_map.c, allowing it to be reused.  It also adds a second tracer
called function_hist that actually does reuse the code, as an RFC
patch.

Patch 01/10 [tracing: Update cond flag when enabling or disabling..]
is a fix for a problem noticed by Daniel and that fixes a problem in
existing trigger code and should be applied regardless of whether the
rest of the patchset is merged.

As mentioned, patch 10/10 is an RFC patch implementing a new tracer
based on the function tracer code.  It's a fun little tool and is
useful for a specific problem I'm working on (and is also a nice test
of the tracing_map code), but is an RFC because first, I'm not sure it
would really be of general interest and secondly, it's POC-level
quality and I'd need to spend more time fixing it up to make it
upstreamable, but I don't want to waste my time if not.

There are a couple of important bits of functionality that were
present in v1 but not yet reimplemented in v5.

The first is support for compound keys.  Currently, maps can only be
keyed on a single event field, whereas in v1 they could be keyed on
multiple keys.  With support for compound keys, you can create much
more interesting output, such as for example per-pid lists of
syscalls or read counts e.g.:

  # echo 'hist:keys=common_pid.execname,id.syscall:vals=hitcount' > \
        /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/trigger

  # cat /sys/kernel/debug/tracing/events/raw_syscalls/sys_enter/hist

  key: common_pid:bash[3112], id:sys_write		       vals: count:69
  key: common_pid:bash[3112], id:sys_rt_sigprocmask	       vals: count:218

  key: common_pid:update-notifier[3164], id:sys_poll	       vals: count:37
  key: common_pid:update-notifier[3164], id:sys_recvfrom       vals: count:118

  key: common_pid:deja-dup-monito[3194], id:sys_sendto	       vals: count:1
  key: common_pid:deja-dup-monito[3194], id:sys_read	       vals: count:4
  key: common_pid:deja-dup-monito[3194], id:sys_poll	       vals: count:8
  key: common_pid:deja-dup-monito[3194], id:sys_recvmsg	       vals: count:8
  key: common_pid:deja-dup-monito[3194], id:sys_getegid	       vals: count:8

  key: common_pid:emacs[3275], id:sys_fsync		       vals: count:1
  key: common_pid:emacs[3275], id:sys_open		       vals: count:1
  key: common_pid:emacs[3275], id:sys_symlink		       vals: count:2
  key: common_pid:emacs[3275], id:sys_poll		       vals: count:23
  key: common_pid:emacs[3275], id:sys_select		       vals: count:23
  key: common_pid:emacs[3275], id:unknown_syscall	       vals: count:34
  key: common_pid:emacs[3275], id:sys_ioctl		       vals: count:60
  key: common_pid:emacs[3275], id:sys_rt_sigprocmask	       vals: count:116

  key: common_pid:cat[3323], id:sys_munmap		       vals: count:1
  key: common_pid:cat[3323], id:sys_fadvise64		       vals: count:1

Related to that is support for sorting on multiple fields.  Currently,
you can sort using only a primary key.  Being able to sort on multiple
or at least a secondary key is indispensible for seeing trends when
displaying multiple values.

Changes from v3:

v4 fixes the race in tracing_map_insert() noted in v3, where
map.val.key could be checked even if map.val wasn't yet set.  The
simple fix for that in tracing_map_insert() introduces the possibility
of duplicates in the map, which though rare, need to be accounted for
in the output.  To address that, duplicate-merging code was added to
the map-printing code.

It was also pointed out that it didn't seem correct to include
module.h, but the fix for that has deeper roots and is being addressed
by a separate patchset; for now we need to continue including
module.h, though prompted by that I did some other header include
cleanup.

The functionality remains the same as v2, but this version no longer
tries to export and use bpf_maps, and more importantly removes the
associated GFP_NOTRACE/trace event hacks and kmem macros required to
work around the bpf_map implementation.

The tracing_map functionality is instead built on top of a simple
lock-free map algorithm originated by Dr. Cliff Click (see references
in the code for more details), which though too restrictive to be
general-purpose in its current form, functions nicely as a
special-purpose tracing map.

v3 also moves the hist triggers code into a separate file and puts it
all behind a new config option, CONFIG_HIST_TRIGGERS.  It also merges
in the sorting code rather than keeping it as a separate patch.

This patchset also includes a couple other new and related triggers,
enable_hist and disable_hist, very similar to the existing
enable_event/disable_event triggers used to automatically enable and
disable events based on a triggering condition, but in this case
allowing hist triggers to be enabled and disabled in the same way.

 - Added an insert check for val before checking the key associated with val
 - Added code to merge possible duplicates in the map

Changes from v2:
 - reimplemented tracing_map, replacing bpf_map with nmi-safe/lock-free map
 - removed GPF_NOTRACE, kmalloc/free macros and event hacks needed by bpf_maps
 - moved hist triggers from trace_events_trigger.c to trace_events_hist.c
 - added CONFIG_HIST_TRIGGERS config option
 - consolidated sorting code with main patch

Changes from v1:
 - completely rewritten on top of tracing_map (renamed and exported bpf_map)
 - added map clearing and client ops to tracing_map
 - changed the name from 'hash' triggers to 'hist' triggers
 - added new trigger 'pause' feature
 - added new enable_hist and disable_hist triggers
 - added usage for hist/enable_hist/disable hist to tracing/README
 - moved examples into Documentation/trace/event.txt
 - added ___GFP_NOTRACE, kmalloc/kfree macros, and conditional kmem tracepoints

The following changes since commit a497adb45b8691f7e477e711a1a4bd54748d64fe:

  ring-buffer: Add enum names for the context levels (2015-05-29 10:39:08 -0400)

are available in the git repository at:

  git://git.yoctoproject.org/linux-yocto-contrib.git tzanussi/hist-triggers-v7
  http://git.yoctoproject.org/cgit/cgit.cgi/linux-yocto-contrib/log/?h=tzanussi/hist-triggers-v7

Tom Zanussi (10):
  tracing: Update cond flag when enabling or disabling a trigger
  tracing: Make ftrace_event_field checking functions available
  tracing: Add event record param to trigger_ops.func()
  tracing: Add get_syscall_name()
  tracing: Add a per-event-trigger 'paused' field
  trace: Add lock-free tracing_map
  tracing: Add 'hist' event trigger command
  tracing: Add enable_hist/disable_hist triggers
  tracing: Add 'hist' trigger Documentation
  ftrace: Add function_hist tracer

 Documentation/trace/events.txt      | 1131 ++++++++++++++++++++++++++++
 include/linux/trace_events.h        |    9 +-
 kernel/trace/Kconfig                |   14 +
 kernel/trace/Makefile               |    3 +
 kernel/trace/trace.c                |   69 ++
 kernel/trace/trace.h                |   88 ++-
 kernel/trace/trace_events.c         |    4 +
 kernel/trace/trace_events_filter.c  |   12 -
 kernel/trace/trace_events_hist.c    | 1407 +++++++++++++++++++++++++++++++++++
 kernel/trace/trace_events_trigger.c |  149 ++--
 kernel/trace/trace_functions_hist.c |  345 +++++++++
 kernel/trace/trace_syscalls.c       |   11 +
 kernel/trace/tracing_map.c          |  920 +++++++++++++++++++++++
 kernel/trace/tracing_map.h          |  143 ++++
 14 files changed, 4221 insertions(+), 84 deletions(-)
 create mode 100644 kernel/trace/trace_events_hist.c
 create mode 100644 kernel/trace/trace_functions_hist.c
 create mode 100644 kernel/trace/tracing_map.c
 create mode 100644 kernel/trace/tracing_map.h

-- 
1.9.3

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