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

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Date:	Sun, 19 Jul 2015 22:47:31 -0700
From:	Brendan Gregg <brendan.d.gregg@...il.com>
To:	Namhyung Kim <namhyung@...nel.org>
Cc:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	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: [RFC PATCH perf/core v2 00/16] perf-probe --cache and SDT support

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. 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.

Brendan
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