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

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Date:	Wed, 26 Feb 2014 18:22:03 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Namhyung Kim <namhyung@...nel.org>,
	Hemant Kumar <hkshaw@...ux.vnet.ibm.com>
Cc:	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: Re: [RFC PATCH v1 0/2] perf: Support for SDT markers

(2014/02/26 17:18), 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.
> 
> 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:*

Ah, that's a good idea :)

>>>
>>> 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. :)

Agreed.

>>>> - 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.

Note that we will need an option to make it permanent (not clear the event on exit)
for people who want to use SDT event from ftrace. :)

>> Will implement the suggestions in the next version asap!
> 
> That would be great!

Thank you!


-- 
Masami HIRAMATSU
IT Management Research Dept. Linux Technology Center
Hitachi, Ltd., Yokohama Research Laboratory
E-mail: masami.hiramatsu.pt@...achi.com


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