linux-kernel - Re: [PATCH RFC] tracing: Call triggers only if event passes filter checks

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Date:   Sun, 17 Jun 2018 17:15:45 -0700
From:   Joel Fernandes <joel@...lfernandes.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Joel Fernandes <joelaf@...gle.com>, linux-kernel@...r.kernel.org,
        kernel-team@...roid.com, Ingo Molnar <mingo@...hat.com>,
        Steven Rostedt <rostedt@...dmis.org>, tglx@...utronix.de,
        namhyung@...nel.org, mathieu.desnoyers@...icios.com,
        linux-rt-users@...r.kernel.org,
        Tom Zanussi <tom.zanussi@...ux.intel.com>, peterz@...radead.org
Subject: Re: [PATCH RFC] tracing: Call triggers only if event passes filter
 checks

On Sat, Jun 16, 2018 at 10:43:29PM +0900, Masami Hiramatsu wrote:
> On Thu, 14 Jun 2018 18:01:13 -0700
> Joel Fernandes <joelaf@...gle.com> wrote:
> 
> > From: "Joel Fernandes (Google)" <joel@...lfernandes.org>
> > 
> > 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
> 

Yes I tried this and it works, thanks!

Steven also suggested the same thing in his reply as well.

thanks,

 - Joel