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SubjectRe: [PATCH v4 8/8] trace: Add alternative synthetic event trace action syntax
Hi Tom,

On Tue, 18 Sep 2018 14:16:43 -0500
Tom Zanussi <zanussi@kernel.org> wrote:

> Hi Masami,
>
> On Wed, 2018-09-19 at 03:54 +0900, Masami Hiramatsu wrote:
> > Hi Tom,
> >
> > On Mon, 10 Sep 2018 14:10:46 -0500
> > Tom Zanussi <zanussi@kernel.org> wrote:
> >
> > > From: Tom Zanussi <tom.zanussi@linux.intel.com>
> > >
> > > Add a 'trace(synthetic_event_name, params)' alternative to
> > > synthetic_event_name(params).
> > >
> > > Currently, the syntax used for generating synthetic events is to
> > > invoke synthetic_event_name(params) i.e. use the synthetic event
> > > name
> > > as a function call.
> > >
> > > Users requested a new form that more explicitly shows that the
> > > synthetic event is in effect being traced. In this version, a new
> > > 'trace()' keyword is used, and the synthetic event name is passed
> > > in
> > > as the first argument.
> >
> > Hmm, what is the advantage of adding this new form?
> >
>
> There's no real advantage other than user preference - Namhyung thought
> that since the event-name-as-function-call actions are all defined as
> ACTION_TRACE, there should also be an explicit 'trace' action.

Ah, got it. Would this needs documentation and testcase update too?

>
> So I added it as alternative syntax - the event-name-as-function-call
> form remains unchanged.
>
> By the way, I also have a patch implementing your alternative syntax
> change, where if you have only one handler, you can do away with the
> explicit action.handler form e.g.
>
> # echo 'hist:keys=next_pid:wakeup_lat=common_timestamp.usecs-ts0: \
> onmax($wakeup_lat): \
> save(next_prio,next_comm,prev_pid,prev_prio,prev_comm):snapshot() \

Hmm, in this case, I think comma-connected syntax will be clearer when
the action is kicked.

onmax($wakeup_lat).save(next_prio,next_comm,prev_pid,prev_prio,prev_comm),snapshot()

any thought?

Thank you,

> if next_comm=="cyclictest"' >> /sys/kernel/debug/tracing/events/sched/sched_switch/trigger
>
> It just wasn't ready to go in with the v4 patches yet, so I decided
> to submit it later as a follow-on.
>
> Tom
>
>
> > Thanks,
> >


--
Masami Hiramatsu <mhiramat@kernel.org>

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