Re: [PATCH v7 00/10] tracing: trace event triggers

[Tom Zanussi <tom.zanussi@linux.intel.com>]

On Tue, 2013-08-27 at 20:35 +0900, Masami Hiramatsu wrote:
> Hi Tom,
> 
> I've reviewed and tested them and found no problem! ;)
> 
> So for this series:
> Reviewed-by: Masami Hiramatsu <masami.hiramatsu.pt@hitachi.com>
> 
> Now, I think it is the time to push it into tracing tree
> and to be widely tested.
> 
> Thank you !

Great, and thank you for the thorough review(s) and testing, Masami!

Tom

> 
> (2013/08/27 12:55), Tom Zanussi wrote:
> > Hi,
> > 
> > This is v7 of the trace event triggers patchset.  This version mainly
> > moves some code between patches to fix some bisectibity problems, but
> > also adds a couple minor cleanups and variable naming changes
> > mentioned by Masami Hiramatsu.
> > 
> > v7:
> >  - moved find_event_file() extern declartion to patch 06.
> >  - moved helper functions from patch 02 to 03, where they're first
> >    used.
> >  - removed copies of cmd_ops fields from trigger_data and changed to
> >    use cmd_ops diretly instead.
> >  - renamed trigger_mode to trigger_type to avoid confusion with the
> >    FTRACE_EVENT_FL_TRIGGER_MODE_BIT bitflag, and fixed up
> >    usage/documentation, etc.
> > 
> > v6:
> >  - fixed up the conflicts in trace_events.c related to the actual
> >    creation of the per-event 'trigger' files.
> > 
> > v5:
> >  - got rid of the trigger_iterator, a vestige of the first patchset,
> >    which attempted to abstract the ftrace_iterator for triggers, and
> >    cleaned up related code simplified as a result.
> >  - replaced the void *cmd_data everywhere with ftrace_event_file *,
> >    another vestige of the initial patchset.
> >  - updated the patchset to use event_file_data() to grab the i_private
> >    ftrace_event_files where appropriate (this was a separate patch in
> >    the previous patchset, but was merged into the basic framework
> >    patch as suggested by Masami.  The only interesting part about this
> >    is that it moved event_file_data() from kernel/trace/trace_events.c
> >    to kernel/trace/trace.h so it can be used in
> >    e.g. trace_events_trigger.c as well.)
> >  - add missing grab of event_mutex in event_trigger_regex_write().
> >  - realized when making the above changes that the trigger filters
> >    weren't being freed when the trigger was freed, so added a
> >    trigger_data_free() to do that.  It also ensures that trigger_data
> >    won't be freed until nothing is using it.
> >  - added clear_event_triggers(), which clears all triggers in a trace
> >    array (and soft-disable associated with event_enable/disable
> >    events).
> >  - added a comment to ftrace_syscall_enter/exit to document the use of
> >    rcu_dereference_raw() there.
> > 
> > v4:
> >  - made some changes to the soft-disable for syscall patch, according
> >    to Masami's suggestions.  Actually, since there's now an array of
> >    ftrace_files for syscalls that can serve the same purpose, the
> >    enabled_enter/exit_syscalls bit arrays became redundant and were
> >    removed.
> >  - moved all the remaining common functions out of the
> >    traceon/traceoff patch and into the basic trigger framework patch
> >    and added comments to all the common functions.
> >  - extensively commented the event_trigger_ops and event_command ops.
> >  - made the register/unregister_command functions __init.  Since that
> >    code was originally inspired by similar ftrace code, a new patch
> >    was added to do the same thing for the register/unregister of the
> >    ftrace commands (patch 10/11).
> >  - fixed the event_trigger_regex_open i_private problem noted by
> >    Masami that's currently being addressed by Oleg Nesterov's fixes
> >    for this.  Note that that patchset also affects patch 8/11 (update
> >    filters for multi-buffer, since it touches event filters as well).
> >    Patch 11/11 depends on that patchset and also moves
> >    event_file_data() to trace.h.b
> > 
> > v3:
> >  - added a new patch to the series (patch 8/9 - update event filters
> >    for multibuffer) to bring the event filters up-to-date wrt the
> >    multibuffer changes - without this patch, the same filter is
> >    applied to all buffers regardless of which instance sets it; this
> >    patch allows you to set per-instance filters as you'd expect.  The
> >    one exception to this is the 'ftrace subsystem' events, which are
> >    special and retain their current behavior.
> >  - changed the syscall soft enabling to keep a per-trace-array array
> >    of trace_event_files alongside the 'enabled' bitmaps there.  This
> >    keeps them in a place where they're only allocated for tracing
> >    and which I think addresses all the previous comments for that
> >    patch.
> > 
> > v2:
> >  - removed all changes to __ftrace_event_enable_disable() (except
> >    for patch 04/11 which clears the soft_disabled bit as discussed)
> >    and created a separate trace_event_trigger_enable_disable() that
> >    calls it after setting/clearing the TRIGGER_MODE_BIT.
> >  - added a trigger_mode enum for future patches that break up the
> >    trigger calls for filtering, but that's also now used as a command
> >    id for registering/unregistering commands.
> >  - removed the enter_file/exit_file members that were added to
> >    syscall_metadata after realizing that they were unnecessary if
> >    ftrace_syscall_enter/exit() were modified to receive a pointer
> >    to the ftrace_file instead of the pointer to the trace_array in
> >    the ftrace_file.
> >  - broke up the trigger invocation into two parts so that triggers
> >    like 'stacktrace' that themselves log into the trace buffer can
> >    defer the actual trigger invocation until after the current
> >    record is closed, which is needed for the filter check that
> >    in turn determines whether the trigger gets invoked.
> >  - other minor cleanup
> > 
> > 
> > This patchset implements 'trace event triggers', which are similar to
> > the function triggers implemented for 'ftrace filter commands' (see
> > 'Filter commands' in Documentation/trace/ftrace.txt), but instead of
> > being invoked from function calls are invoked by trace events.
> > Basically the patchset allows 'commands' to be triggered whenever a
> > given trace event is hit.  The set of commands implemented by this
> > patchset are:
> > 
> >  - enable/disable_event - enable or disable another event whenever
> >    the trigger event is hit
> > 
> >  - stacktrace - dump a stacktrace to the trace buffer whenever the
> >    trigger event is hit
> > 
> >  - snapshot - create a snapshot of the current trace buffer whenever
> >    the trigger event is hit
> > 
> >  - traceon/traceoff - turn tracing on or off whenever the trigger
> >    event is hit
> > 
> > Triggers can also be conditionally invoked by associating a standard
> > trace event filter with them - if the given event passes the filter,
> > the trigger is invoked, otherwise it's not. (see 'Event filtering' in
> > Documentation/trace/events.txt for info on event filters).
> > 
> > See the last patch in the series for more complete documention on
> > event triggers and the available trigger commands, and below for some
> > simple examples of each of the above commands along with conditional
> > filtering.
> > 
> > The first four patches are bugfix patches or minor improvements which
> > can be applied regardless; the rest contain the basic framework and
> > implementations for each command.
> > 
> > This patchset was based on some ideas from Steve Rostedt, which he
> > outlined during a couple discussions at ELC and follow-on e-mails.
> > Code- and interface-wise, it's also partially based on the existing
> > function triggers implementation and essentially works on top of the
> > SOFT_DISABLE mode introduced for that.  Both Steve and Masami
> > Hiramatsu took a look at a couple early versions of this patchset, and
> > offered some very useful suggestions reflected in this patchset -
> > thanks to them both for the ideas and for taking the time to do some
> > basic sanity reviews!
> > 
> > Below are a few concrete examples demonstrating each of the available
> > commands.
> > 
> > The first example attempts to capture all the kmalloc events that
> > happen as a result of reading a particular file.
> > 
> > The first part of the set of commands below adds a kmalloc
> > 'enable_event' trigger to the sys_enter_read trace event - as a
> > result, when the sys_enter_read event occurs, kmalloc events are
> > enabled, resulting in those kmalloc events getting logged into the
> > trace buffer.  The :1 at the end of the kmalloc enable_event specifies
> > that the enabling of kmalloc events on sys_enter_read will only happen
> > once - subsequent reads won't trigger the kmalloc logging.  The next
> > part of the example reads a test file, which triggers the
> > sys_enter_read tracepoint and thus turns on the kmalloc events, and
> > once done, adds a trigger to sys_exit_read that disables kmalloc
> > events.  The disable_event doesn't have a :1 appended, which means it
> > happens on every sys_exit_read.
> > 
> > # echo 'enable_event:kmem:kmalloc:1' > \
> >   /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/trigger; \
> >   cat ~/junk.txt > /dev/null; \
> >   echo 'disable_event:kmem:kmalloc' > \
> >   /sys/kernel/debug/tracing/events/syscalls/sys_exit_read/trigger
> > 
> > Just to show a bit of what happens under the covers, if we display the
> > kmalloc 'enable' file, we see that it's 'soft disabled' (the asterisk
> > after the enable flag).  This means that it's actually enabled but is
> > in the SOFT_DISABLED state, and is essentially held back from actually
> > logging anything to the trace buffer, but can be made to log into the
> > buffer by simply flipping a bit :
> > 
> > # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/enable
> > 0*
> > 
> > If we look at the 'enable' file for the triggering sys_enter_read
> > trace event, we can see that it also has the 'soft disable' flag set.
> > This is because in the case of the triggering event, we also need to
> > have the trace event invoked regardless of whether or not its actually
> > being logged, so we can process the triggers.  This functionality is
> > also built on top of the SOFT_DISABLE flag and is reflected in the
> > enable state as well:
> > 
> > # cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/enable
> > 0*
> > 
> > To find out which triggers are set for a particular event, we can look
> > at the 'trigger' file for the event.  Here's what the 'trigger' file
> > for the sys_enter_read event looks like:
> > 
> > # cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/trigger
> > enable_event:kmem:kmalloc:count=0
> > 
> > The 'count=0' field at the end shows that this trigger has no more
> > triggering ability left - it's essentially fired all its shots - if
> > it was still active, it would have a non-zero count.
> > 
> > Looking at the sys_exit_read, we see that since we didn't specify a
> > number at the end, the number of times it can fire is unlimited:
> > 
> > # cat /sys/kernel/debug/tracing/events/syscalls/sys_exit_read/trigger
> > disable_event:kmem:kmalloc:unlimited
> > 
> > # cat /sys/kernel/debug/tracing/events/syscalls/sys_exit_read/enable
> > 0*
> > 
> > Finally, let's look at the results of the above set of commands by
> > cat'ing the 'trace' file:
> > 
> > # cat /sys/kernel/debug/tracing/trace
> > 
> > # tracer: nop
> > #
> > # entries-in-buffer/entries-written: 85/85   #P:4
> > #
> > #                              _-----=> irqs-off
> > #                             / _----=> need-resched
> > #                            | / _---=> hardirq/softirq
> > #                            || / _--=> preempt-depth
> > #                            ||| /     delay
> > #           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
> > #              | |       |   ||||       |         |
> >              cat-2596  [001] ....   374.518849: kmalloc: call_site=ffffffff812de707 ptr=ffff8800306b9290 bytes_req=2 bytes_alloc=8 gfp_flags=GFP_KERNEL|GFP_ZERO
> >              cat-2596  [001] ....   374.518956: kmalloc: call_site=ffffffff81182a12 ptr=ffff88010c8e1500 bytes_req=256 bytes_alloc=256 gfp_flags=GFP_KERNEL|GFP_ZERO
> >              cat-2596  [001] ....   374.518959: kmalloc: call_site=ffffffff812d8e49 ptr=ffff88003002a200 bytes_req=32 bytes_alloc=32 gfp_flags=GFP_KERNEL|GFP_ZERO
> >              cat-2596  [001] ....   374.518960: kmalloc: call_site=ffffffff812de707 ptr=ffff8800306b9088 bytes_req=2 bytes_alloc=8 gfp_flags=GFP_KERNEL|GFP_ZERO
> >              cat-2596  [003] ....   374.519063: kmalloc: call_site=ffffffff812d9f50 ptr=ffff8800b793fd00 bytes_req=256 bytes_alloc=256 gfp_flags=GFP_KERNEL
> >              cat-2596  [003] ....   374.519119: kmalloc: call_site=ffffffff811cc3bc ptr=ffff8800b7918900 bytes_req=128 bytes_alloc=128 gfp_flags=GFP_KERNEL
> >              cat-2596  [003] ....   374.519122: kmalloc: call_site=ffffffff811cc4d2 ptr=ffff880030404800 bytes_req=504 bytes_alloc=512 gfp_flags=GFP_KERNEL
> >              cat-2596  [003] ....   374.519125: kmalloc: call_site=ffffffff811cc64e ptr=ffff88003039d8a0 bytes_req=28 bytes_alloc=32 gfp_flags=GFP_KERNEL
> > .
> > .
> > .
> >             Xorg-1194  [000] ....   374.543956: kmalloc: call_site=ffffffffa03a8599 ptr=ffff8800ba23b700 bytes_req=112 bytes_alloc=128 gfp_flags=GFP_TEMPORARY|GFP_NOWARN|GFP_NORETRY
> >             Xorg-1194  [000] ....   374.543961: kmalloc: call_site=ffffffffa03a7639 ptr=ffff8800b7905b40 bytes_req=56 bytes_alloc=64 gfp_flags=GFP_TEMPORARY|GFP_ZERO
> >             Xorg-1194  [000] ....   374.543973: kmalloc: call_site=ffffffffa039f716 ptr=ffff8800b7905ac0 bytes_req=64 bytes_alloc=64 gfp_flags=GFP_KERNEL
> > .
> > .
> > .
> >           compiz-1769  [002] ....   374.547586: kmalloc: call_site=ffffffffa03a8599 ptr=ffff8800ba320400 bytes_req=952 bytes_alloc=1024 gfp_flags=GFP_TEMPORARY|GFP_NOWARN|GFP_NORETRY
> >           compiz-1769  [002] ....   374.547592: kmalloc: call_site=ffffffffa03a7639 ptr=ffff8800bd5f7400 bytes_req=280 bytes_alloc=512 gfp_flags=GFP_TEMPORARY|GFP_ZERO
> >           compiz-1769  [002] ....   374.547623: kmalloc: call_site=ffffffffa039f716 ptr=ffff8800b792d580 bytes_req=64 bytes_alloc=64 gfp_flags=GFP_KERNEL
> > .
> > .
> > .
> >              cat-2596  [000] ....   374.646019: kmalloc: call_site=ffffffff8123df9f ptr=ffff8800ba2f2900 bytes_req=96 bytes_alloc=96 gfp_flags=GFP_NOFS|GFP_ZERO
> >              cat-2596  [000] ....   374.648263: kmalloc: call_site=ffffffff8123df9f ptr=ffff8800ba2f2900 bytes_req=96 bytes_alloc=96 gfp_flags=GFP_NOFS|GFP_ZERO
> >              cat-2596  [000] ....   374.650503: kmalloc: call_site=ffffffff8123df9f ptr=ffff8800ba2f2900 bytes_req=96 bytes_alloc=96 gfp_flags=GFP_NOFS|GFP_ZERO
> > .
> > .
> > .
> >             bash-2425  [002] ....   374.654923: kmalloc: call_site=ffffffff8123df9f ptr=ffff8800b7a28780 bytes_req=96 bytes_alloc=96 gfp_flags=GFP_NOFS|GFP_ZERO
> >         rsyslogd-974   [002] ....   374.655163: kmalloc: call_site=ffffffff81046ae6 ptr=ffff8800ba320400 bytes_req=1024 bytes_alloc=1024 gfp_flags=GFP_KERNEL
> > 
> > As you can see, we captured all the kmallocs from our 'cat' reads, but
> > also any other kmallocs that happened for other processes between the
> > time we turned on kmalloc events and turned them off.  Future work
> > should add a way to screen out unwanted events e.g. the abilitiy to
> > capture the triggering pid in a simple variable and use that variable
> > in event filters to screen out other pids.
> > 
> > To turn off the events we turned on, simply reinvoke the commands
> > prefixed by '!':
> > 
> > # echo '!enable_event:kmem:kmalloc:1' > /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/trigger
> > # echo '!disable_event:kmem:kmalloc' > /sys/kernel/debug/tracing/events/syscalls/sys_exit_read/trigger
> > 
> > You can verify that the events have been turned off by again examining
> > the 'enable' and 'trigger' files:
> > 
> > # cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/trigger
> > # cat /sys/kernel/debug/tracing/events/syscalls/sys_enter_read/enable
> > 0
> > # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/enable
> > 0
> > 
> > 
> > The next example shows how to use the 'stacktrace' command.  To have a
> > stacktrace logged every time a particular event occurs, simply echo
> > 'stacktrace' into the 'trigger' file for that event:
> > 
> > # echo 'stacktrace' > /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
> > 
> > # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
> > stacktrace:unlimited
> > 
> > Looking at the 'trace' output, we indeed see stack traces for every
> > kmalloc:
> > 
> > # cat /sys/kernel/debug/tracing/trace
> > 
> >           compiz-1769  [003] ....  2422.614630: <stack trace>
> >  => i915_add_request
> >  => i915_gem_do_execbuffer.isra.15
> >  => i915_gem_execbuffer2
> >  => drm_ioctl
> >  => do_vfs_ioctl
> >  => SyS_ioctl
> >  => system_call_fastpath
> >             Xorg-1194  [002] ....  2422.619076: <stack trace>
> >  => drm_wait_vblank
> >  => drm_ioctl
> >  => do_vfs_ioctl
> >  => SyS_ioctl
> >  => system_call_fastpath
> >             Xorg-1194  [000] ....  2422.625823: <stack trace>
> >  => i915_gem_execbuffer2
> >  => drm_ioctl
> >  => do_vfs_ioctl
> >  => SyS_ioctl
> >  => system_call_fastpath
> > .
> > .
> > .
> >             bash-2842  [001] ....  2423.002059: <stack trace>
> >  => __tracing_open
> >  => tracing_open
> >  => do_dentry_open
> >  => finish_open
> >  => do_last
> >  => path_openat
> >  => do_filp_open
> >  => do_sys_open
> >  => SyS_open
> >  => system_call_fastpath
> >             bash-2842  [001] ....  2423.002070: <stack trace>
> >  => __tracing_open
> >  => tracing_open
> >  => do_dentry_open
> >  => finish_open
> >  => do_last
> >  => path_openat
> >  => do_filp_open
> >  => do_sys_open
> >  => SyS_open
> >  => system_call_fastpath
> > 
> > For an event like kmalloc, however, we don't typically want to see a
> > stack trace for every single event, since the amount of data produced
> > is overwhelming.  What we'd typically want to do is only log a stack
> > trace for particular events of interest.  We can accomplish that by
> > appending an 'event filter' to the trigger.  The event filters used to
> > filter triggers are exactly the same as those implemented for the
> > existing trace event 'filter' files - see the trace event
> > documentation for details.
> > 
> > First, let's turn off the existing stacktrace event, and clear the
> > trace buffer:
> > 
> > # echo '!stacktrace' > /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
> > # echo > /sys/kernel/debug/tracing/trace
> > 
> > Now, we can add a new stacktrace trigger which will fire 5 times, but
> > only if the number of bytes requested by the caller was greater than
> > or equal to 512:
> > 
> > # echo 'stacktrace:5 if bytes_req >= 512' > \
> >      /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
> > 
> > # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
> > stacktrace:count=0 if bytes_req >= 512
> > 
> >>From looking at the trigger, we can see the event fired 5 times
> > (count=0) and looking at the 'trace' file, we can verify that:
> > 
> > # cat trace
> > # tracer: nop
> > #
> > # entries-in-buffer/entries-written: 5/5   #P:4
> > #
> > #                              _-----=> irqs-off
> > #                             / _----=> need-resched
> > #                            | / _---=> hardirq/softirq
> > #                            || / _--=> preempt-depth
> > #                            ||| /     delay
> > #           TASK-PID   CPU#  ||||    TIMESTAMP  FUNCTION
> > #              | |       |   ||||       |         |
> >         rsyslogd-974   [000] ....  1796.412997: <stack trace>
> >  => kmem_cache_alloc_trace
> >  => do_syslog
> >  => kmsg_read
> >  => proc_reg_read
> >  => vfs_read
> >  => SyS_read
> >  => system_call_fastpath
> >           compiz-1769  [000] ....  1796.427342: <stack trace>
> >  => __kmalloc
> >  => i915_gem_execbuffer2
> >  => drm_ioctl
> >  => do_vfs_ioctl
> >  => SyS_ioctl
> >  => system_call_fastpath
> >             Xorg-1194  [003] ....  1796.441251: <stack trace>
> >  => __kmalloc
> >  => i915_gem_execbuffer2
> >  => drm_ioctl
> >  => do_vfs_ioctl
> >  => SyS_ioctl
> >  => system_call_fastpath
> >             Xorg-1194  [003] ....  1796.441392: <stack trace>
> >  => __kmalloc
> >  => sg_kmalloc
> >  => __sg_alloc_table
> >  => sg_alloc_table
> >  => i915_gem_object_get_pages_gtt
> >  => i915_gem_object_get_pages
> >  => i915_gem_object_pin
> >  => i915_gem_execbuffer_reserve_object.isra.11
> >  => i915_gem_execbuffer_reserve
> >  => i915_gem_do_execbuffer.isra.15
> >  => i915_gem_execbuffer2
> >  => drm_ioctl
> >  => do_vfs_ioctl
> >  => SyS_ioctl
> >  => system_call_fastpath
> >             Xorg-1194  [003] ....  1796.441672: <stack trace>
> >  => __kmalloc
> >  => i915_gem_execbuffer2
> >  => drm_ioctl
> >  => do_vfs_ioctl
> >  => SyS_ioctl
> >  => system_call_fastpath
> > 
> > So the trace output shows exactly 5 stacktraces, as expected.
> > 
> > Just for comparison, let's look at an event that's harder to trigger,
> > to see a count that isn't 0 in the trigger description:
> > 
> > # echo 'stacktrace:5 if bytes_req >= 65536' > \
> >      /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
> > 
> > # cat /sys/kernel/debug/tracing/events/kmem/kmalloc/trigger
> > stacktrace:count=5 if bytes_req >= 65536
> > 
> > 
> > The next example shows how to use the 'snapshot' command to capture a
> > snapshot of the trace buffer when an 'interesting' event occurs.
> > 
> > In this case, we'll first start the entire block subsystem tracing:
> > 
> > # echo 1 > /sys/kernel/debug/tracing/events/block/enable
> > 
> > Next, we add a 'snapshot' trigger that will take a snapshot of all the
> > events leading up to the particular event we're interested in, which
> > is a block queue unplug with a depth > 1.  In this case we're
> > interested in capturing the snapshot just one time, the first time it
> > occurs:
> > 
> > # echo 'snapshot:1 if nr_rq > 1' > \
> >      /sys/kernel/debug/tracing/events/block/block_unplug/trigger
> > 
> > It may take awhile for the condition to occur, but once it does, we
> > can see the entire sequence of block events leading up to in in the
> > 'snapshot' file:
> > 
> > # cat /sys/kernel/debug/tracing/snapshot
> > 
> >      jbd2/sdb1-8-278   [001] ....   382.075012: block_bio_queue: 8,16 WS 629429976 + 8 [jbd2/sdb1-8]
> >      jbd2/sdb1-8-278   [001] ....   382.075012: block_bio_backmerge: 8,16 WS 629429976 + 8 [jbd2/sdb1-8]
> >      jbd2/sdb1-8-278   [001] d...   382.075015: block_rq_insert: 8,16 WS 0 () 629429912 + 72 [jbd2/sdb1-8]
> >      jbd2/sdb1-8-278   [001] d...   382.075030: block_rq_issue: 8,16 WS 0 () 629429912 + 72 [jbd2/sdb1-8]
> >      jbd2/sdb1-8-278   [001] d...   382.075044: block_unplug: [jbd2/sdb1-8] 1
> >           <idle>-0     [000] ..s.   382.075310: block_rq_complete: 8,16 WS () 629429912 + 72 [0]
> >      jbd2/sdb1-8-278   [000] ....   382.075407: block_touch_buffer: 8,17 sector=78678492 size=4096
> >      jbd2/sdb1-8-278   [000] ....   382.075413: block_bio_remap: 8,16 FWFS 629429984 + 8 <- (8,17) 629427936
> >      jbd2/sdb1-8-278   [000] ....   382.075415: block_bio_queue: 8,16 FWFS 629429984 + 8 [jbd2/sdb1-8]
> >      jbd2/sdb1-8-278   [000] ....   382.075418: block_getrq: 8,16 FWFS 629429984 + 8 [jbd2/sdb1-8]
> >      jbd2/sdb1-8-278   [000] d...   382.075421: block_rq_insert: 8,16 FWFS 0 () 629429984 + 8 [jbd2/sdb1-8]
> >      jbd2/sdb1-8-278   [000] d...   382.075424: block_rq_issue: 8,16 FWS 0 () 18446744073709551615 + 0 [jbd2/sdb1-8]
> >           <idle>-0     [000] dNs.   382.115912: block_rq_issue: 8,16 WS 0 () 629429984 + 8 [swapper/0]
> >           <idle>-0     [000] ..s.   382.116059: block_rq_complete: 8,16 WS () 629429984 + 8 [0]
> >           <idle>-0     [000] dNs.   382.116079: block_rq_issue: 8,16 FWS 0 () 18446744073709551615 + 0 [swapper/0]
> >           <idle>-0     [000] d.s.   382.131030: block_rq_complete: 8,16 WS () 629429984 + 0 [0]
> >      jbd2/sdb1-8-278   [000] ....   382.131106: block_dirty_buffer: 8,17 sector=26 size=4096
> >      jbd2/sdb1-8-278   [000] ....   382.131111: block_dirty_buffer: 8,17 sector=106954757 size=4096
> > .
> > .
> > .
> >    kworker/u16:3-66    [002] ....   387.144505: block_bio_remap: 8,16 WM 2208 + 8 <- (8,17) 160
> >    kworker/u16:3-66    [002] ....   387.144512: block_bio_queue: 8,16 WM 2208 + 8 [kworker/u16:3]
> >    kworker/u16:3-66    [002] ....   387.144522: block_getrq: 8,16 WM 2208 + 8 [kworker/u16:3]
> >    kworker/u16:3-66    [002] ....   387.144525: block_plug: [kworker/u16:3]
> >    kworker/u16:3-66    [002] ....   387.144530: block_bio_remap: 8,16 WM 2216 + 8 <- (8,17) 168
> >    kworker/u16:3-66    [002] ....   387.144531: block_bio_queue: 8,16 WM 2216 + 8 [kworker/u16:3]
> >    kworker/u16:3-66    [002] ....   387.144533: block_bio_backmerge: 8,16 WM 2216 + 8 [kworker/u16:3]
> > .
> > .
> > .
> >    kworker/u16:3-66    [002] d...   387.144631: block_rq_insert: 8,16 WM 0 () 2208 + 16 [kworker/u16:3]
> >    kworker/u16:3-66    [002] d...   387.144636: block_rq_insert: 8,16 WM 0 () 2256 + 16 [kworker/u16:3]
> >    kworker/u16:3-66    [002] d...   387.144638: block_rq_insert: 8,16 WM 0 () 662702080 + 8 [kworker/u16:3]
> >    kworker/u16:3-66    [002] d...   387.144640: block_rq_insert: 8,16 WM 0 () 683673680 + 8 [kworker/u16:3]
> >    kworker/u16:3-66    [002] d...   387.144641: block_rq_insert: 8,16 WM 0 () 729812344 + 8 [kworker/u16:3]
> >    kworker/u16:3-66    [002] d...   387.144642: block_rq_insert: 8,16 WM 0 () 729828896 + 8 [kworker/u16:3]
> >    kworker/u16:3-66    [002] d...   387.144643: block_rq_insert: 8,16 WM 0 () 730599480 + 8 [kworker/u16:3]
> >    kworker/u16:3-66    [002] d...   387.144644: block_rq_insert: 8,16 WM 0 () 855640104 + 8 [kworker/u16:3]
> >    kworker/u16:3-66    [002] d...   387.144645: block_rq_insert: 8,16 WM 0 () 880805984 + 8 [kworker/u16:3]
> >    kworker/u16:3-66    [002] d...   387.144646: block_rq_insert: 8,16 WM 0 () 1186990400 + 8 [kworker/u16:3]
> >    kworker/u16:3-66    [002] d...   387.144649: block_unplug: [kworker/u16:3] 10
> > 
> > 
> > The final example shows something very similer but using the
> > 'traceoff' command to stop tracing when an 'interesting' event occurs.
> > The traceon and traceoff commands can be used together to toggle
> > tracing on and off in creative ways to capture different traces in the
> > 'trace' buffer, but this example just shows essentially the same use
> > case as the previous example but using 'traceoff' to capture trace
> > data of interest in the standard 'trace' buffer.
> > 
> > Again, we'll start the entire block subsystem tracing:
> > 
> > # echo 1 > /sys/kernel/debug/tracing/events/block/enable
> > 
> > # echo 'traceoff:1 if nr_rq > 1' > \
> >      /sys/kernel/debug/tracing/events/block/block_unplug/trigger
> > 
> > # cat /sys/kernel/debug/tracing/trace
> > 
> >    kworker/u16:4-67    [000] ....   803.003670: block_bio_remap: 8,16 WM 2208 + 8 <- (8,17) 160
> >    kworker/u16:4-67    [000] ....   803.003670: block_bio_queue: 8,16 WM 2208 + 8 [kworker/u16:4]
> >    kworker/u16:4-67    [000] ....   803.003672: block_getrq: 8,16 WM 2208 + 8 [kworker/u16:4]
> >    kworker/u16:4-67    [000] ....   803.003674: block_bio_remap: 8,16 WM 2216 + 8 <- (8,17) 168
> >    kworker/u16:4-67    [000] ....   803.003675: block_bio_queue: 8,16 WM 2216 + 8 [kworker/u16:4]
> >    kworker/u16:4-67    [000] ....   803.003676: block_bio_backmerge: 8,16 WM 2216 + 8 [kworker/u16:4]
> >    kworker/u16:4-67    [000] ....   803.003678: block_bio_remap: 8,16 WM 2232 + 8 <- (8,17) 184
> >    kworker/u16:4-67    [000] ....   803.003678: block_bio_queue: 8,16 WM 2232 + 8 [kworker/u16:4]
> >    kworker/u16:4-67    [000] ....   803.003680: block_getrq: 8,16 WM 2232 + 8 [kworker/u16:4]
> > .
> > .
> > .
> >    kworker/u16:4-67    [000] d...   803.003720: block_rq_insert: 8,16 WM 0 () 285223776 + 16 [kworker/u16:4]
> >    kworker/u16:4-67    [000] d...   803.003721: block_rq_insert: 8,16 WM 0 () 662702080 + 8 [kworker/u16:4]
> >    kworker/u16:4-67    [000] d...   803.003722: block_rq_insert: 8,16 WM 0 () 683673680 + 8 [kworker/u16:4]
> >    kworker/u16:4-67    [000] d...   803.003723: block_rq_insert: 8,16 WM 0 () 730599480 + 8 [kworker/u16:4]
> >    kworker/u16:4-67    [000] d...   803.003724: block_rq_insert: 8,16 WM 0 () 763365384 + 8 [kworker/u16:4]
> >    kworker/u16:4-67    [000] d...   803.003725: block_rq_insert: 8,16 WM 0 () 880805984 + 8 [kworker/u16:4]
> >    kworker/u16:4-67    [000] d...   803.003726: block_rq_insert: 8,16 WM 0 () 1186990872 + 8 [kworker/u16:4]
> >    kworker/u16:4-67    [000] d...   803.003727: block_rq_insert: 8,16 WM 0 () 1187057608 + 8 [kworker/u16:4]
> >    kworker/u16:4-67    [000] d...   803.003729: block_unplug: [kworker/u16:4] 14
> > 
> > The following changes since commit fc30f13b7c1b87b44ee364462c3408c913f01439:
> > 
> >   Merge branch 'trace/ftrace/core-tpstring' into trace/for-next (2013-08-22 12:30:55 -0400)
> > 
> > are available in the git repository at:
> > 
> > 
> >   git://git.yoctoproject.org/linux-yocto-contrib.git tzanussi/event-triggers-v6
> >   http://git.yoctoproject.org/cgit/cgit.cgi/linux-yocto-contrib/log/?h=tzanussi/event-triggers-v7
> > 
> > Tom Zanussi (10):
> >   tracing: Add support for SOFT_DISABLE to syscall events
> >   tracing: add basic event trigger framework
> >   tracing: add 'traceon' and 'traceoff' event trigger commands
> >   tracing: add 'snapshot' event trigger command
> >   tracing: add 'stacktrace' event trigger command
> >   tracing: add 'enable_event' and 'disable_event' event trigger
> >     commands
> >   tracing: add and use generic set_trigger_filter() implementation
> >   tracing: update event filters for multibuffer
> >   tracing: add documentation for trace event triggers
> >   tracing: make register/unregister_ftrace_command __init
> > 
> >  Documentation/trace/events.txt       |  207 +++++
> >  include/linux/ftrace.h               |    4 +-
> >  include/linux/ftrace_event.h         |   56 +-
> >  include/trace/ftrace.h               |   39 +-
> >  kernel/trace/Makefile                |    1 +
> >  kernel/trace/ftrace.c                |   12 +-
> >  kernel/trace/trace.c                 |   31 +-
> >  kernel/trace/trace.h                 |  194 ++++-
> >  kernel/trace/trace_branch.c          |    2 +-
> >  kernel/trace/trace_events.c          |   49 +-
> >  kernel/trace/trace_events_filter.c   |  181 ++++-
> >  kernel/trace/trace_events_trigger.c  | 1402 ++++++++++++++++++++++++++++++++++
> >  kernel/trace/trace_export.c          |    2 +-
> >  kernel/trace/trace_functions_graph.c |    4 +-
> >  kernel/trace/trace_kprobe.c          |    4 +-
> >  kernel/trace/trace_mmiotrace.c       |    4 +-
> >  kernel/trace/trace_sched_switch.c    |    4 +-
> >  kernel/trace/trace_syscalls.c        |   62 +-
> >  kernel/trace/trace_uprobe.c          |    3 +-
> >  19 files changed, 2142 insertions(+), 119 deletions(-)
> >  create mode 100644 kernel/trace/trace_events_trigger.c
> > 
> 
>