linux-kernel - Re: [PATCH v3 5/5] perf/sdt: Add support to perf record to trace SDT events

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Message-ID: <20141023055422.GA27939@linux.vnet.ibm.com>
Date:	Thu, 23 Oct 2014 11:24:22 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
Cc:	Hemant Kumar <hemant@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, peterz@...radead.org,
	oleg@...hat.com, hegdevasant@...ux.vnet.ibm.com, mingo@...hat.com,
	anton@...hat.com, systemtap@...rceware.org, namhyung@...nel.org,
	aravinda@...ux.vnet.ibm.com, penberg@....fi
Subject: Re: [PATCH v3 5/5] perf/sdt: Add support to perf record to trace SDT
 events

* Masami Hiramatsu <masami.hiramatsu.pt@...achi.com> [2014-10-22 18:41:58]:

> (2014/10/22 17:20), Hemant Kumar wrote:
> >>> From "file_sdt_ent" we will find out the file name.
> >>> Convert this sdt note into a perf event and then write this into uprobe_events
> >>> file to be able to record the event.
> >>> Then, corresponding entries are added to uprobe_events file for
> >>> the SDT events.
> >>> After recording is done, these events are silently deleted from uprobe_events
> >>> file. The uprobe_events file is present in debugfs/tracing directory.
> >>>
> >>> To support the addition and deletion of SDT events to/from uprobe_events
> >>> file, a record_sdt struct is maintained which has the event data.
> >> OK, I have some comments on this.
> >>
> >>> An example usage:
> >>>
> >>> # ./perf record -e %user_app:fun_start -aR /home/user_app
> >> At first, I'd like to add SDT support for adding probes too, like below;
> >>
> >> ./perf probe -a '%user_app:fun_start $vars'
> >
> > But I think, previously we discussed that we won't be having "perf
> > probe" for SDT events.
> > We list them and probe/trace them using "perf record" directly.
>
> Right, sorry for confusing you. I meant that I'd like to support SDT on both of
> perf-record and perf-probe :)
> And even if we'll hide sdt related events via perf, users can access it via ftrace.
> So, I doubt that we can completely hide them, in that case, honesty is the best way;)
>

I am somehow not able to figure out how perf probe comes into the
current workflow.

I think the current design was
1. perf sdt-cache --add <file> (only once per file)
2. perf record -e <sdt-event>

So what is the additional thing that perf probe does or Is it going to
replace any of the above steps?

--
Thanks and Regards
Srikar Dronamraju

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