On Fri, 3 May 2019 17:35:37 +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. Hi Tzvetomir, Thanks for sending this. Some minor tweaks below. > > Signed-off-by: Tzvetomir Stoyanov <tstoyanov@xxxxxxxxxx> > --- > Documentation/trace/histogram.txt | 11 +++++++---- > 1 file changed, 7 insertions(+), 4 deletions(-) > > diff --git a/Documentation/trace/histogram.txt b/Documentation/trace/histogram.txt > index 7ffea6aa22e3..b75a75cfab8c 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 case > + multiple histogram keys are used, they all must match in the specified > + order. I would reword that to be: In the case that 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 +1923,9 @@ 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 (saved_pid matches next_pid), calculate CPU by a sched_switch event (where the sched_waking key "saved_pid" matches the sched_switch key "next_pid"), Other than that, looks good. Could you send a v2 with the updates? Thanks! -- Steve > + 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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