diff options
| author | Steven Rostedt (Red Hat) <rostedt@goodmis.org> | 2013-03-12 21:26:18 +0400 |
|---|---|---|
| committer | Steven Rostedt <rostedt@goodmis.org> | 2013-03-15 08:36:03 +0400 |
| commit | 417944c4c7a0f657158d0515f3b8e8c043fd788f (patch) | |
| tree | 838e9bb09f8df63af3adf5b865d3781eeac8d6ba /include/linux/ftrace_event.h | |
| parent | 7818b3886545f89549185e4023743e2df91d1fa1 (diff) | |
| download | linux-417944c4c7a0f657158d0515f3b8e8c043fd788f.tar.xz | |
tracing: Add a way to soft disable trace events
In order to let triggers enable or disable events, we need a 'soft'
method for doing so. For example, if a function probe is added that
lets a user enable or disable events when a function is called, that
change must be done without taking locks or a mutex, and definitely
it can't sleep. But the full enabling of a tracepoint is expensive.
By adding a 'SOFT_DISABLE' flag, and converting the flags to be updated
without the protection of a mutex (using set/clear_bit()), this soft
disable flag can be used to allow critical sections to enable or disable
events from being traced (after the event has been placed into "SOFT_MODE").
Some caveats though: The comm recorder (to map pids with a comm) can not
be soft disabled (yet). If you disable an event with with a "soft"
disable and wait a while before reading the trace, the comm cache may be
replaced and you'll get a bunch of <...> for comms in the trace.
Reading the "enable" file for an event that is disabled will now give
you "0*" where the '*' denotes that the tracepoint is still active but
the event itself is "disabled".
[ fixed _BIT used in & operation : thanks to Dan Carpenter and smatch ]
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Diffstat (limited to 'include/linux/ftrace_event.h')
| -rw-r--r-- | include/linux/ftrace_event.h | 20 |
1 files changed, 14 insertions, 6 deletions
diff --git a/include/linux/ftrace_event.h b/include/linux/ftrace_event.h index 4cb6cd8338a4..4e28b011e63b 100644 --- a/include/linux/ftrace_event.h +++ b/include/linux/ftrace_event.h @@ -251,16 +251,23 @@ struct ftrace_subsystem_dir; enum { FTRACE_EVENT_FL_ENABLED_BIT, FTRACE_EVENT_FL_RECORDED_CMD_BIT, + FTRACE_EVENT_FL_SOFT_MODE_BIT, + FTRACE_EVENT_FL_SOFT_DISABLED_BIT, }; /* * Ftrace event file flags: * ENABLED - The event is enabled * RECORDED_CMD - The comms should be recorded at sched_switch + * SOFT_MODE - The event is enabled/disabled by SOFT_DISABLED + * SOFT_DISABLED - When set, do not trace the event (even though its + * tracepoint may be enabled) */ enum { FTRACE_EVENT_FL_ENABLED = (1 << FTRACE_EVENT_FL_ENABLED_BIT), FTRACE_EVENT_FL_RECORDED_CMD = (1 << FTRACE_EVENT_FL_RECORDED_CMD_BIT), + FTRACE_EVENT_FL_SOFT_MODE = (1 << FTRACE_EVENT_FL_SOFT_MODE_BIT), + FTRACE_EVENT_FL_SOFT_DISABLED = (1 << FTRACE_EVENT_FL_SOFT_DISABLED_BIT), }; struct ftrace_event_file { @@ -274,17 +281,18 @@ struct ftrace_event_file { * 32 bit flags: * bit 0: enabled * bit 1: enabled cmd record + * bit 2: enable/disable with the soft disable bit + * bit 3: soft disabled * - * Changes to flags must hold the event_mutex. - * - * Note: Reads of flags do not hold the event_mutex since - * they occur in critical sections. But the way flags + * Note: The bits must be set atomically to prevent races + * from other writers. Reads of flags do not need to be in + * sync as they occur in critical sections. But the way flags * is currently used, these changes do not affect the code * except that when a change is made, it may have a slight * delay in propagating the changes to other CPUs due to - * caching and such. + * caching and such. Which is mostly OK ;-) */ - unsigned int flags; + unsigned long flags; }; #define __TRACE_EVENT_FLAGS(name, value) \ |