Re: [GIT PULL 0/8] perf/pt -> Intel PT/BTS

Arnaldo Carvalho de Melo
2015-06-30T14:39:32Z

Em Tue, Jun 30, 2015 at 04:23:45PM +0300, Adrian Hunter escreveu:
> On 30/06/15 13:56, Ingo Molnar wrote:
> >
> > * Adrian Hunter <adrian.hunter@intel.com> wrote:
> >
> >>> Yeah, so I did a 'newbie test':
> >>>
> >>> I pulled the tree and saw that it has a tools/perf/Documentation/intel-bts.txt
> >>> file and started reading it.
> >>>
> >>> Based on its text:
> >>>
> >>> The Intel BTS kernel driver creates a new PMU for Intel BTS. The perf record
> >>> option is:
> >>>
> >>> -e intel_bts//
> >>>
> >>> Currently Intel BTS is limited to per-thread tracing so the --per-thread option
> >>> is also needed.
> >>>
> >>> I tried the following command which failed:
> >>>
> >>> triton:~/tip> perf record -e intel_bts// --per-thread sleep 1
> >>> invalid or unsupported event: 'intel_bts//'
> >>> Run 'perf list' for a list of valid events
> >>>
> >>> usage: perf record [<options>] [<command>]
> >>> or: perf record [<options>] -- <command> [<options>]
> >>>
> >>> -e, --event <event> event selector. use 'perf list' to list available events
> >>>
> >>> That's a really ... unhelpful message. If I typoed something I want to know that.
> >>> If the kernel does not support something, I want to know about that too. Tooling
> >>> telling me: "maybe you typoed something, maybe it's not supported, I really don't
> >>> care" is not very productive.
> >>
> >> That is not entirely true. The message says "Run 'perf list' for a list of valid
> >> events" which will tell you if the event is valid. So you can tell the
> >> difference between a typo and unsupported event.
> >
> > Yeah, but my point is: why doesn't the tool do this disambiguation for me? Tools
> > are hard enough to use as-is already, no need to put artificial roadblocks in the
> > path of first time users.
>
> That applies to all events e.g.
>
> # perf record -e sched:sched_swotch sleep 1
> invalid or unsupported event: 'sched:sched_swotch'
> Run 'perf list' for a list of valid events
>
> usage: perf record [<options>] [<command>]
> or: perf record [<options>] -- <command> [<options>]
>
> -e, --event <event> event selector. use 'perf list' to list available events
>
> So it is a general problem.

Right, guess it is interesting to note at this point that Jiri improved
this area:

[acme@zoo linux]$ perf record -e sched:sched_swotch sleep 1
event syntax error: 'sched:sched_swotch'
\___ unknown tracepoint
Run 'perf list' for a list of valid events

usage: perf record [<options>] [<command>]
or: perf record [<options>] -- <command> [<options>]

-e, --event <event> event selector. use 'perf list' to list available events
[acme@zoo linux]$

But:

[acme@zoo linux]$ perf record -e intel_pt// usleep 1
invalid or unsupported event: 'intel_pt//'
Run 'perf list' for a list of valid events

usage: perf record [<options>] [<command>]
or: perf record [<options>] -- <command> [<options>]

-e, --event <event> event selector. use 'perf list' to list available events
[acme@zoo linux]$

I'll investigate how this can be improved...

- Arnaldo