linux-kernel - Re: [RFC PATCH perf/core v2 15/16] perf buildid-cache: Scan and import user SDT events to probe cache

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Date:	Tue, 21 Jul 2015 19:42:30 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Namhyung Kim <namhyung@...nel.org>
CC:	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-kernel@...r.kernel.org,
	Adrian Hunter <adrian.hunter@...el.com>,
	Ingo Molnar <mingo@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	Jiri Olsa <jolsa@...nel.org>, Borislav Petkov <bp@...e.de>,
	Hemant Kumar <hemant@...ux.vnet.ibm.com>
Subject: Re: [RFC PATCH perf/core v2 15/16] perf buildid-cache: Scan and import
 user SDT events to probe cache

On 2015/07/21 0:52, Namhyung Kim wrote:
> On Mon, Jul 20, 2015 at 12:19:14PM +0900, Masami Hiramatsu wrote:
>> On 2015/07/19 19:46, Namhyung Kim wrote:
>>> On Wed, Jul 15, 2015 at 06:15:37PM +0900, Masami Hiramatsu wrote:
>>>> perf buildid-cache --add <binary> scans given binary and add
>>>> the SDT events to probe cache. It is possible to use the cached
>>>> SDT events as other cached events (perf probe <provider>:<event>=<event>).
>>>
>>> That means lookup the cached SDT events only using event name, right?
>>
>> Right,
>>
>>> What if same event names are used by more than one providers?
>>
>> That's a good discussion point :)
>>
>> What I'm thinking is that the real SDT is always prior to other
>> cached events. (currently not implemented yet)
>>  - if someone gives a same event name, it overwrites previous one.
>>  - if someone gives an event name same as existing SDT, it is not
>>    cached (or rejected)
>>  - if SDT scanned after cached same name events, SDT always overwrites
>>    the entry.
> 
> I'm thinking about allowing same name for different events.  IMHO it's
> possible to have same SDT names for some reason - i.e. having multiple
> versions of same program, similar (but different) binaries have same
> event names, or even in a single bianry it might have same event names
> but different provider names.
> 
> In that case, I think perf probe (or record) simply can do the job for
> every matching events.

Hmm, right. If we support the 3-level event name as you said, that
can make things much simpler. We can use "probe_<12chars-buildid>"
for the toplevel dirname, and "provider/name" for lower 2 levels.

Or, if we can use <provider>.<buildid>/ for the group name (this requres
kernel change) it is more easier to support SDTs.

Thank you,

> 
>>
>> So, the all SDT events will be treated as fixed events.
>>
>> Note that this will be happen if we agree SDT and probe share the
>> same namespace :)
> 
> Right.
> 
> Thanks,
> Namhyung
> 
> 


-- 
Masami HIRAMATSU
Linux Technology Research Center, System Productivity Research Dept.
Center for Technology Innovation - Systems Engineering
Hitachi, Ltd., Research & Development Group
E-mail: masami.hiramatsu.pt@...achi.com
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