linux-kernel - Re: [RFC PATCH v1 0/2] perf: Support for SDT markers

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Date:	Wed, 26 Feb 2014 14:33:39 +0530
From:	Hemant Kumar <hkshaw@...ux.vnet.ibm.com>
To:	Namhyung Kim <namhyung@...nel.org>
CC:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	linux-kernel@...r.kernel.org, srikar@...ux.vnet.ibm.com,
	peterz@...radead.org, oleg@...hat.com,
	hegdevasant@...ux.vnet.ibm.com, mingo@...hat.com, anton@...hat.com,
	systemtap@...rceware.org, aravinda@...ux.vnet.ibm.com,
	penberg@....fi
Subject: Re: [RFC PATCH v1 0/2] perf: Support for SDT markers

On 02/26/2014 01:48 PM, Namhyung Kim wrote:
> Hi Masami and Hemant,
>
> On Tue, 25 Feb 2014 21:27:07 +0530, Hemant Kumar wrote:
>> On 02/25/2014 05:14 PM, Masami Hiramatsu wrote:
>>> (2014/02/24 18:14), Hemant Kumar wrote:
>>>> First, scan the binaries using :
>>>> # perf list sdt --scan
>>>>
>>>> Creating a cache of SDT markers...
>>>> perf sdt cache created!
>>>>    Use : "perf list sdt"
>>>>    to see the SDT markers
>>> Hmm, in that case, I think you'd better introduce perf-sdt for scanning.
>>> e.g.
>>>
>>>    # perf sdt --scan app
>> Hmm, this seems a better idea :)
>>
>>>    then you can add app to sdt cache, without app,
>>>
>>>    # perf sdt --scan
>>>
>>>    will just scans all binaries on the PATH and the libraries which listed
>>> by `ldconfig --print-caceh`
> What should be done with the new perf sdt command?  If it's only
> intended to list the markers, I'd just suggest to add "perf list sdt" as
> this patch did.

If we display the SDT markers along with the other events in perf list, 
then I think we can go with
perf list sdt. I am not too sure though! :)

For me, the main issue was that the markers are not events. They become 
events after
we place them in the uprobe_events file just like functions.  But we use 
`perf list` to
display all the "events" available on a system. Isn't it?

> Plus I think it'd be better if event_glob pattern also looks for sdt
> markers so that user can find out a specific markers easily, e.g.:
>
>    # perf list rtld:*
>
> or
>
>    # perf list %rtld:*

Good idea! Will surely include support for this in event_glob pattern.

>>> And perf-list shows only the SDTs in the cache.
>> Well, what will be better? perf-list or perf-sdt or perf-list sdt??
>> If perf-list, then wouldn't it be a huge list!!
> The output of perf list is already a huge list and we paginate it.  So I
> don't think it's gonna be a problem. :)

Ok! Then we can use perf list. :)

>
>>>> - Add support to probe these SDT markers and integrate with a previous patch
>>>>     (support to perf to probe SDT markers) posted in lkml.
>>>>     https://lkml.org/lkml/2013/10/23/10
>>> Yeah, but I think we'd better choose another way to integrate it.
>>> Since SDT is like markers(static events), setting each of them via perf-probe is
>>> not intuitive. :)  I'd like to use it as an event, e.g.
>>>
>>>    # perf top -e "%libgcc:unwind"
>>>
>>> And perf top internally calls perf-probe to add new uprobe event, and
>>> clean the new event at exit.
>> Yeah! Right :) Makes sense.
>>
>> Will implement the suggestions in the next version asap!
> That would be great!

-- 
Thanks
Hemant Kumar

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