linux-kernel - Re: Re: Re: [RFC PATCH perf/core v2 00/16] perf-probe --cache and SDT support

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Date:	Tue, 21 Jul 2015 19:34:14 +0900
From:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>
To:	Namhyung Kim <namhyung@...nel.org>,
	Brendan Gregg <brendan.d.gregg@...il.com>
CC:	Hemant Kumar <hemant@...ux.vnet.ibm.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <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>
Subject: Re: Re: Re: [RFC PATCH perf/core v2 00/16] perf-probe --cache
 and SDT support

On 2015/07/21 1:20, Namhyung Kim wrote:
> Hi Brendan,
> 
> On Sun, Jul 19, 2015 at 10:47:31PM -0700, Brendan Gregg wrote:
>> G'Day Masami-san, Namhyung,
>>
>> I'm really looking forward to this feature -- very useful, thanks!...
>>
>> On Sat, Jul 18, 2015 at 9:24 PM, Namhyung Kim <namhyung@...nel.org> wrote:
>>> Hi Masami,
>>>
>>> On Fri, Jul 17, 2015 at 12:21:42PM +0900, Masami Hiramatsu wrote:
>>>> Now I'm thinking that we should avoid using %event syntax for perf-list
>>>> and perf-record to avoid confusion. For example, suppose that we have
>>>> "libfoo:bar" SDT event, when we just scanned the libfoo binary and
>>>> use it via perf-record, we'll run perf record -e "%libfoo:bar".
>>>> However, after we set the probe via perf-probe, we have to run
>>>> perf record -e "libfoo:bar". That difference looks no good.
>>>> So, I think in both case it should accept -e "libfoo:bar" syntax.
>>>
>>> I don't remember how the SDT events should be shown to users.  Sorry
>>> if I'm missing something here.
>>>
>>> AFAIK an SDT event consists of a provider and an event name.  So it
>>> can be simply 'provider:event' like tracepoints or
>>> 'binary:provider_event' like uprobes.
>>>
>>> I like the former because it's simpler but it needs to guarantee that
>>> it doesn't clash with existing tracepoints/[ku]probes.  So IIUC we
>>> chose the '%' sign to distinguish them.  But after setting a probe at
>>> it, the group name should be the binary name.  So the whole event name
>>> might be changed, and this is not good.
>>
>> I don't think we should worry about the clash, as the provider name
>> should differentiate.
> 
> But there's no guarantee.  Maybe an userspace tool which deals with a
> kernel module has SDT names as same as the kernel module's tracepoint
> names.  It might or might not be a problem if we can handle those
> duplicate names somehow.

I'd like to suggest to choose the behavior on scanning SDT. Since the
perf-probe just relays on what the event names are stored on the cache file,
we can choose "sdt_" prefix or not when scanning the SDT.
If the name is already used by the kernel tracepoint, we can add sdt_ prefix
or some sort of suffix.

Thank you,

>> So I think "libfoo:bar" with perf record is
>> better. After adding them to the cache (via % if needed), I'd think
>> they would be best looking like tracepoints. Eg, listing them together
>> they can be differentiated, something like:
>>
>> # perf list
>> [...]
>>   block:block_rq_abort                               [Tracepoint event]
>>   block:block_rq_requeue                             [Tracepoint event]
>>   block:block_rq_complete                            [Tracepoint event]
>> [...]
>>   libc:memory_heap_new                                [User tracepoint event]
>>   libc:memory_heap_free                               [User tracepoint event]
>>   libc:memory_heap_more                               [User tracepoint event]
>> [...]
>>
>> Then used the same.
> 
> Yes, as I said I also prefer this simpler form.  Maybe we can choose
> to use another names for low-level plumbing inside the perf tools, but
> I still think that users should be able to use simple names like above.


-- 
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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