Tom, Can you review this patch. Jon, After Tom gives his review, can you take this in your tree? Thanks! Reviewed-by: Steven Rostedt (VMware) <rostedt@xxxxxxxxxxx> -- Steve On Tue, 7 May 2019 17:49:46 +0300 Tzvetomir Stoyanov <tstoyanov@xxxxxxxxxx> wrote: > The current trace documentation, the section describing histogram's "onmatch" > is not straightforward enough about how this action is applied. It is not > clear what criteria are used to "match" both events. A short note is added, > describing what exactly is compared in order to match the events. > > Signed-off-by: Tzvetomir Stoyanov <tstoyanov@xxxxxxxxxx> > --- > Documentation/trace/histogram.txt | 12 ++++++++---- > 1 file changed, 8 insertions(+), 4 deletions(-) > > diff --git a/Documentation/trace/histogram.txt b/Documentation/trace/histogram.txt > index 7ffea6aa22e3..d97f0530a731 100644 > --- a/Documentation/trace/histogram.txt > +++ b/Documentation/trace/histogram.txt > @@ -1863,7 +1863,10 @@ hist trigger specification. > > The 'matching.event' specification is simply the fully qualified > event name of the event that matches the target event for the > - onmatch() functionality, in the form 'system.event_name'. > + onmatch() functionality, in the form 'system.event_name'. Histogram > + keys of both events are compared to find if events match. In the case > + multiple histogram keys are used, both events must have the same > + number of keys, and the keys must match in the same order. > > Finally, the number and type of variables/fields in the 'param > list' must match the number and types of the fields in the > @@ -1920,9 +1923,10 @@ hist trigger specification. > /sys/kernel/debug/tracing/events/sched/sched_waking/trigger > > Then, when the corresponding thread is actually scheduled onto the > - CPU by a sched_switch event, calculate the latency and use that > - along with another variable and an event field to generate a > - wakeup_latency synthetic event: > + CPU by a sched_switch event (where the sched_waking key "saved_pid" > + matches the sched_switch key "next_pid"), calculate the latency and > + use that along with another variable and an event field to generate > + a wakeup_latency synthetic event: > > # echo 'hist:keys=next_pid:wakeup_lat=common_timestamp.usecs-$ts0:\ > onmatch(sched.sched_waking).wakeup_latency($wakeup_lat,\
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