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

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Date:	Wed, 26 Feb 2014 21:41:51 +0530
From:	Hemant Kumar <hkshaw@...ux.vnet.ibm.com>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
CC:	Namhyung Kim <namhyung@...nel.org>, 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 03:12 PM, Masami Hiramatsu wrote:
> (2014/02/26 18:03), Hemant Kumar wrote:
>> 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.
> No, here what I said is, the "perf sdt" is only for managing SDT cache
> as like as "perf buildid-cache". Thus, "perf sdt-cache" might be better.

Ah! ok.

> BTW, the SDT markers can be changed if the application is updated.
> To ensure the correctness of SDT markers, we should store buildid in the
> cache file and check it when listing and using them.

Yeah! That's why perf list sdt --scan is storing the buildid too in the 
cache file.

>> 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?
> As I said, if perf accepts -e "%app:sdt" option, showing SDT events as
> fixed events does not matter, since it is transparent to users. :)
>
> Thank you,
>

Alright. Got it! :)

-- 
Thanks
Hemant Kumar

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