On Thu, 14 Jun 2018 18:01:13 -0700
Joel Fernandes [off-list ref] wrote:

From: "Joel Fernandes (Google)" <redacted>

Currently, trace event triggers are called regardless of if the event
filter checks pass or fail. Thus if one were to enable event triggers
and filters at the same time, then the triggers will always be called
even if the filter checks didn't pass.

This is a problem for a usecase I was experimenting with: measuring the
time preemption is disabled using synthetic events and dump the stack
using the stacktrace trigger if the total preempt off time was greater
than a threshold. Following are the commands for the same:

Create synthetic event:

echo 'preemptdisable u64 lat' >> \
	      /sys/kernel/debug/tracing/synthetic_events

echo 'hist:keys=cpu:ts0=common_timestamp.usecs:scpu=cpu' >> \
	      /sys/kernel/debug/tracing/events/preemptirq/preempt_disable/trigger

echo 'hist:keys=cpu:wakeup_lat=common_timestamp.usecs-$ts0:\
onmatch(preemptirq.preempt_disable).preemptdisable($wakeup_lat)' >> \
	        /sys/kernel/debug/tracing/events/preemptirq/preempt_enable/trigger

Enable synthetic event:

echo stacktrace > /sys/kernel/debug/tracing/events/synthetic/preemptdisable/trigger
echo 'lat > 400' > /sys/kernel/debug/tracing/events/synthetic/preemptdisable/filter

Have you tried if statement as below?

echo "stacktrace if lat > 400" > /sys/kernel/debug/tracing/events/synthetic/preemptdisable/trigger

As my understanding, filter is used for controlling "recording the event"
and trigger is out of its scope. Trigger itself has own filter as
"if statement", so you should use it.

Thank you,


-- 
Masami Hiramatsu [off-list ref]