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SubjectRe: [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@hitachi.com


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