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

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Message-ID: <530DB6FE.9020307@hitachi.com>
Date:	Wed, 26 Feb 2014 18:42:22 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Hemant Kumar <hkshaw@...ux.vnet.ibm.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: Re: [RFC PATCH v1 0/2] perf: Support for SDT markers

(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.

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.

> 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,

-- 
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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