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: <20150720155207.GB9265@danjae.kornet>
Date:	Tue, 21 Jul 2015 00:52:07 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
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 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.

> 
> 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

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