diff options
| author | Tom Zanussi <tom.zanussi@linux.intel.com> | 2018-01-15 20:51:56 -0600 |
|---|---|---|
| committer | Steven Rostedt (VMware) <rostedt@goodmis.org> | 2018-03-10 16:05:58 -0500 |
| commit | 067fe038e70f6e64960d26a79c4df5f1413d0f13 (patch) | |
| tree | 57e3c474f63b54b5a20494b2344a28efa0b9f976 /kernel/trace/trace.c | |
| parent | 19a9facd0fe33a3e376923383958b2c86cbd3994 (diff) | |
tracing: Add variable reference handling to hist triggers
Add the necessary infrastructure to allow the variables defined on one
event to be referenced in another. This allows variables set by a
previous event to be referenced and used in expressions combining the
variable values saved by that previous event and the event fields of
the current event. For example, here's how a latency can be
calculated and saved into yet another variable named 'wakeup_lat':
# echo 'hist:keys=pid,prio:ts0=common_timestamp ...
# echo 'hist:keys=next_pid:wakeup_lat=common_timestamp-$ts0 ...
In the first event, the event's timetamp is saved into the variable
ts0. In the next line, ts0 is subtracted from the second event's
timestamp to produce the latency.
Further users of variable references will be described in subsequent
patches, such as for instance how the 'wakeup_lat' variable above can
be displayed in a latency histogram.
Link: http://lkml.kernel.org/r/b1d3e6975374e34d501ff417c20189c3f9b2c7b8.1516069914.git.tom.zanussi@linux.intel.com
Signed-off-by: Tom Zanussi <tom.zanussi@linux.intel.com>
Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Diffstat (limited to 'kernel/trace/trace.c')
| -rw-r--r-- | kernel/trace/trace.c | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c index 82cc8891fda6..68f8702af9fb 100644 --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -7783,6 +7783,7 @@ static int instance_mkdir(const char *name) INIT_LIST_HEAD(&tr->systems); INIT_LIST_HEAD(&tr->events); + INIT_LIST_HEAD(&tr->hist_vars); if (allocate_trace_buffers(tr, trace_buf_size) < 0) goto out_free_tr; @@ -8533,6 +8534,7 @@ __init static int tracer_alloc_buffers(void) INIT_LIST_HEAD(&global_trace.systems); INIT_LIST_HEAD(&global_trace.events); + INIT_LIST_HEAD(&global_trace.hist_vars); list_add(&global_trace.list, &ftrace_trace_arrays); apply_trace_boot_options(); |