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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Message-ID: <55AC68B2.6080905@hitachi.com>
Date:	Mon, 20 Jul 2015 12:19:14 +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 2015/07/19 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.

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 :)

>>
>> e.g.
>>   ----
>>   # perf buildid-cache --add /lib/libc-2.17.so
>>   # perf probe --cache --list | head -n 5
>>   /usr/lib/libc-2.17.so (a6fb821bdf53660eb2c29f778757aef294d3d392):
>>   libc:setjmp=setjmp
>>   libc:longjmp=longjmp
>>   libc:longjmp_target=longjmp_target
>>   libc:memory_heap_new=memory_heap_new
> 
> I expected something like this instead..
> 
>     libc:memory_heap_new=new_heap+183

OK, that's much better :)

> 
> 
> Thanks,
> Namhyung
> 
> 
>>   # perf probe -x /usr/lib/libc-2.17.so \
>>     -a libc:memory_heap_new=memory_heap_new
>>   Added new event:
>>     libc:memory_heap_new (on memory_heap_new
>>    in /usr/lib/libc-2.17.so)
>>
>>   You can now use it in all perf tools, such as:
>>
>>           perf record -e libc:memory_heap_new -aR sleep 1
>>
>>   # perf probe -l
>>     libc:memory_heap_new (on new_heap+183 in /usr/lib/libc-2.17.so)
>>   ----
>>
>> Note that SDT event entries in probe-cache file is somewhat different
>> from normal cached events. Normal one starts with "#", but SDTs are
>> starting with "%".
>>
>> Signed-off-by: Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
> 


-- 
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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