Date:	Thu, 10 Dec 2015 12:54:18 -0600
From:	Tom Zanussi <tom.zanussi@...ux.intel.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	rostedt@...dmis.org, daniel.wagner@...-carit.de,
	masami.hiramatsu.pt@...achi.com, josh@...htriplett.org,
	andi@...stfloor.org, mathieu.desnoyers@...icios.com,
	peterz@...radead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 00/30] tracing: 'hist' triggers

On Mon, 2015-11-30 at 00:22 +0900, Namhyung Kim wrote:
> On Mon, Nov 23, 2015 at 01:51:15PM -0600, Tom Zanussi wrote:
> > This is v12 of the 'hist triggers' patchset, incorporating suggestions
> > and fixing problems pointed out by Namhyung.
> 
> Thanks for doing this work!  This version looks good to me although I
> have a small nitpick in the 10/30.  With that fixed, you can add my
> 
>   Reviewed-by: Namhyung Kim <namhyung@...nel.org>
> 
> to this patchset.
> 

Thanks for your review, Namhyung - I just posted a new patchset with
that fix..

Tom

> Thanks,
> Namhyung
> 
> 
> > 
> > Changes from v11:
> > 
> >   - Added tracing_map_lookup().
> >   - Changed tracing_map_insert() to incorporate the hits/drops counter
> >     updating.  The changes allow clients to continue calling
> >     tracing_map_insert() and update existing entries if desired, or
> >     stop on the first drop, since the return value is still NULL in
> >     that case.
> >   - Changed the hist trigger code to continue calling
> >     tracing_map_insert() rather than stopping on the first drop.  The
> >     idea is that there's no harm in continuing after the first drop -
> >     if the user can't tolerate any drops, they'll still see a non-zero
> >     drop count and can retry with a larger table, but if the user
> >     doesn't care, the hit and drop counts are an accurate reflection
> >     of how many events were tallied vs dropped.
> >   - Added a new unreg_all() callback to event_command, and code to
> >     call it when the trigger file is opened for truncate.  Implemented
> >     unreg_all() for hist triggers, which allows them to honor the
> >     truncate flag while leaving existing triggers intact.  This means
> >     that '>>' should now be used for adding multiple hist triggers as
> >     well as to clear/pause/cont an existing hist trigger.
> >   - Included Namhyung's log2 patch.
> >   - Fixed one of Masami's test cases which now requires using '>>' due
> >     to the truncate changes.
> >   - 'cont' and 'clear' no longer create a trigger if one doesn't exist.
> >   - Rebased to latest trace/for-next.
> >   - Various other smaller fixes and Documentation updates as noted by
> >     Namhyung.
> > 
> > Changes from v10:
> > 
> >   - Rebased to latest trace/for-next.
> >   - Added Masami's ftrace/hist triggers kselftest patches.
> >   - Added Masami's Tested-by: to the series.
> > 
> > Changes from v9:
> > 
> > v10 adds some major new features - 'named' hist triggers and support
> > for multiple hist triggers on a single event - basically all of the
> > features and suggestions suggested by Masami, except for one: I
> > decided after all not to implement the 'pause/continue/clear' commands
> > on the hist file.  I've gotten so used to the habit of calling up the
> > previous trigger-setting command in the command history and simply
> > appending a 'pause/cont/clear' command to it (and later removing it by
> > prepending a '!') that making the user change the command doesn't seem
> > as naturally usable.  Masami, if you disagree, let me know and I'll
> > reconsider it but at this point I'd rather not make that change.
> > 
> > In addition, I think I've fixed all the other various smaller problems
> > mentioned in the previous review, please let me know if I missed any...
> > 
> >   - Added support for 'named' hist triggers
> >   - Added support for multiple hist triggers on a single trace event
> >   - Added documentation and examples for the above new features
> >   - Streamlined the README to only include the essentials for hist triggers
> >   - Fixed the 'hex' modifier for values, which was previously ignored
> >   - Replaced the kmalloc of large arrays with a simple page-based scheme
> >   - Fixed the tracing_map_insert() case where jhash returns 0
> >   - Fixed various other small problems noted along the way
> > 
> > Changes from v8:
> > 
> > Same as v8, but with the RFC patch [ftrace: Add function_hist tracer]
> > removed, and rebased to latest trace/for-next.
> > 
> > Changes from v7:
> > 
> > This version refactors the commits as suggested by Masami.  There are
> > now more commits, but the result should be much more reviewable.  The
> > ending code is the same as before, modulo a couple minor bug fixes I
> > discovered while refactoring and testing.
> > 
> > I've also reviewed and fixed a number of shortcomings and errors in
> > the comments, and have added a new discussion of the tracing_map data
> > structures after Steve mentioned he found them confusing and/or
> > insufficiently documented.
> > 
> > Also, I kept Namhyung's string patch [tracing: Support string type key
> > properly] as submitted, but added a follow-on patch that refactors it
> > and fixes a problem I found with it that enabled static string keys to
> > contain random chars and therefore incorrect map insertions.
> > 
> > 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 e428abbbf616cd8fdd1162e4a624ad1d47b47544:
> > 
> >   tracing: #ifdef out uses of max trace when CONFIG_TRACER_MAX_TRACE is not set (2015-11-10 10:16:05 -0500)
> > 
> > are available in the git repository at:
> > 
> >   git://git.yoctoproject.org/linux-yocto-contrib.git tzanussi/hist-triggers-v12
> >   http://git.yoctoproject.org/cgit/cgit.cgi/linux-yocto-contrib/log/?h=tzanussi/hist-triggers-v12
> > 
> > Masami Hiramatsu (2):
> >   kselftests/ftrace : Add event trigger testcases
> >   kselftests/ftrace: Add hist trigger testcases
> > 
> > Namhyung Kim (2):
> >   tracing: Support string type key properly
> >   tracing: Add hist trigger 'log2' modifier
> > 
> > Tom Zanussi (26):
> >   tracing: Update cond flag when enabling or disabling a trigger
> >   tracing: Make ftrace_event_field checking functions available
> >   tracing: Make event trigger functions available
> >   tracing: Add event record param to trigger_ops.func()
> >   tracing: Add get_syscall_name()
> >   tracing: Add a per-event-trigger 'paused' field
> >   tracing: Add needs_rec flag to event triggers
> >   tracing: Add an unreg_all() callback to trigger commands
> >   tracing: Add lock-free tracing_map
> >   tracing: Add 'hist' event trigger command
> >   tracing: Add hist trigger support for multiple values ('vals=' param)
> >   tracing: Add hist trigger support for compound keys
> >   tracing: Add hist trigger support for user-defined sorting ('sort='
> >     param)
> >   tracing: Add hist trigger support for pausing and continuing a trace
> >   tracing: Add hist trigger support for clearing a trace
> >   tracing: Add hist trigger 'hex' modifier for displaying numeric fields
> >   tracing: Add hist trigger 'sym' and 'sym-offset' modifiers
> >   tracing: Add hist trigger 'execname' modifier
> >   tracing: Add hist trigger 'syscall' modifier
> >   tracing: Add hist trigger support for stacktraces as keys
> >   tracing: Remove restriction on string position in hist trigger keys
> >   tracing: Add enable_hist/disable_hist triggers
> >   tracing: Add 'hist' trigger Documentation
> >   tracing: Add support for multiple hist triggers per event
> >   tracing: Add support for named triggers
> >   tracing: Add support for named hist triggers
> > 
> >  Documentation/trace/events.txt                     | 1555 ++++++++++++++++++
> >  include/linux/trace_events.h                       |    9 +-
> >  kernel/trace/Kconfig                               |   27 +
> >  kernel/trace/Makefile                              |    2 +
> >  kernel/trace/trace.c                               |   57 +
> >  kernel/trace/trace.h                               |  106 +-
> >  kernel/trace/trace_events.c                        |    4 +
> >  kernel/trace/trace_events_filter.c                 |   12 -
> >  kernel/trace/trace_events_hist.c                   | 1731 ++++++++++++++++++++
> >  kernel/trace/trace_events_trigger.c                |  309 +++-
> >  kernel/trace/trace_syscalls.c                      |   11 +
> >  kernel/trace/tracing_map.c                         | 1058 ++++++++++++
> >  kernel/trace/tracing_map.h                         |  282 ++++
> >  tools/testing/selftests/ftrace/test.d/functions    |    9 +
> >  .../ftrace/test.d/trigger/trigger-eventonoff.tc    |   64 +
> >  .../ftrace/test.d/trigger/trigger-filter.tc        |   59 +
> >  .../ftrace/test.d/trigger/trigger-hist-mod.tc      |   65 +
> >  .../ftrace/test.d/trigger/trigger-hist.tc          |   83 +
> >  .../ftrace/test.d/trigger/trigger-multihist.tc     |   73 +
> >  .../ftrace/test.d/trigger/trigger-snapshot.tc      |   56 +
> >  .../ftrace/test.d/trigger/trigger-stacktrace.tc    |   53 +
> >  .../ftrace/test.d/trigger/trigger-traceonoff.tc    |   58 +
> >  22 files changed, 5596 insertions(+), 87 deletions(-)
> >  create mode 100644 kernel/trace/trace_events_hist.c
> >  create mode 100644 kernel/trace/tracing_map.c
> >  create mode 100644 kernel/trace/tracing_map.h
> >  create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/trigger-eventonoff.tc
> >  create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/trigger-filter.tc
> >  create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/trigger-hist-mod.tc
> >  create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/trigger-hist.tc
> >  create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/trigger-multihist.tc
> >  create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/trigger-snapshot.tc
> >  create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/trigger-stacktrace.tc
> >  create mode 100644 tools/testing/selftests/ftrace/test.d/trigger/trigger-traceonoff.tc
> > 
> > -- 
> > 1.9.3
> > 


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