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

[Namhyung Kim <namhyung@kernel.org>]

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@kernel.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.


> 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.

Thanks,
Namhyung