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

[Ingo Molnar <mingo@kernel.org>]

* Arnaldo Carvalho de Melo <acme@kernel.org> wrote:

> Hi Ingo,
> 
> 	Please consider pulling, there are several other patches after this,
> but I think that this may be acceptable to showcase the capabilities already
> present, look at the output of 'perf script' and callchains for userspace
> without using any extra debugging info (no need for DWARF, CFI, nothing),
> really cool capabilities... :-)
> 
> 	Adrian wrote some docs and I tested it both on a Ivy Bridge machine
> where there is only BTS and on a Broadwell machine with the whole shebang,
> adding the output of the commands to the csets, to further showcase what is
> there already.
> 
> 	This is on top of my last perf-core-for-mingo tag.
> 
> 	Up to you, please let us know what you think and we'll continue working
> on having this in an acceptable form for merging,
> 
> Regards,
> 
> - Arnaldo
> 
> P.S. Kudos for Adrian for the patience with this process, way more is needed to
> polish this, but the promise is there, cool stuff indeed! :-)
> 
> The following changes since commit 36c8bb56a9f718a9a5f35d1834ca9dcec95deb4a:
> 
>   perf symbols: Check access permission when reading symbol files (2015-06-26 12:11:53 -0300)
> 
> are available in the git repository at:
> 
>   git://git.kernel.org/pub/scm/linux/kernel/git/acme/linux.git tags/perf-pt-for-mingo
> 
> for you to fetch changes up to 04759f172270afb28c8004f5cad62ed55710a499:
> 
>   perf tools: Add Intel BTS support (2015-06-26 18:36:11 -0300)
> 
> ----------------------------------------------------------------
> Put Intel PT and BTS into initial use (Adrian Hunter)
> 
> Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
> 
> ----------------------------------------------------------------
> Adrian Hunter (8):
>       perf auxtrace: Add Intel PT as an AUX area tracing type
>       perf tools: Add Intel PT packet decoder
>       perf tools: Add Intel PT instruction decoder
>       perf tools: Add Intel PT log
>       perf tools: Add Intel PT decoder
>       perf tools: Add Intel PT support
>       perf tools: Take Intel PT into use
>       perf tools: Add Intel BTS support
> 
>  tools/build/Makefile.build                         |    2 +
>  tools/perf/.gitignore                              |    2 +
>  tools/perf/Documentation/intel-bts.txt             |   86 +
>  tools/perf/Documentation/intel-pt.txt              |  588 ++++++
>  tools/perf/MANIFEST                                |    7 +
>  tools/perf/Makefile.perf                           |   12 +-
>  tools/perf/arch/x86/util/Build                     |    5 +
>  tools/perf/arch/x86/util/auxtrace.c                |   83 +
>  tools/perf/arch/x86/util/intel-bts.c               |  458 +++++
>  tools/perf/arch/x86/util/intel-pt.c                |  752 ++++++++
>  tools/perf/arch/x86/util/pmu.c                     |   18 +
>  tools/perf/util/Build                              |    3 +
>  tools/perf/util/auxtrace.c                         |    9 +-
>  tools/perf/util/auxtrace.h                         |    2 +
>  tools/perf/util/intel-bts.c                        |  791 ++++++++
>  tools/perf/util/intel-bts.h                        |   43 +
>  tools/perf/util/intel-pt-decoder/Build             |   14 +
>  .../perf/util/intel-pt-decoder/intel-pt-decoder.c  | 1759 ++++++++++++++++++
>  .../perf/util/intel-pt-decoder/intel-pt-decoder.h  |  102 ++
>  .../util/intel-pt-decoder/intel-pt-insn-decoder.c  |  246 +++
>  .../util/intel-pt-decoder/intel-pt-insn-decoder.h  |   65 +
>  tools/perf/util/intel-pt-decoder/intel-pt-log.c    |  155 ++
>  tools/perf/util/intel-pt-decoder/intel-pt-log.h    |   52 +
>  .../util/intel-pt-decoder/intel-pt-pkt-decoder.c   |  400 +++++
>  .../util/intel-pt-decoder/intel-pt-pkt-decoder.h   |   64 +
>  tools/perf/util/intel-pt.c                         | 1889 ++++++++++++++++++++
>  tools/perf/util/intel-pt.h                         |   51 +
>  tools/perf/util/pmu.c                              |    4 -
>  28 files changed, 7655 insertions(+), 7 deletions(-)
>  create mode 100644 tools/perf/Documentation/intel-bts.txt
>  create mode 100644 tools/perf/Documentation/intel-pt.txt
>  create mode 100644 tools/perf/arch/x86/util/auxtrace.c
>  create mode 100644 tools/perf/arch/x86/util/intel-bts.c
>  create mode 100644 tools/perf/arch/x86/util/intel-pt.c
>  create mode 100644 tools/perf/arch/x86/util/pmu.c
>  create mode 100644 tools/perf/util/intel-bts.c
>  create mode 100644 tools/perf/util/intel-bts.h
>  create mode 100644 tools/perf/util/intel-pt-decoder/Build
>  create mode 100644 tools/perf/util/intel-pt-decoder/intel-pt-decoder.c
>  create mode 100644 tools/perf/util/intel-pt-decoder/intel-pt-decoder.h
>  create mode 100644 tools/perf/util/intel-pt-decoder/intel-pt-insn-decoder.c
>  create mode 100644 tools/perf/util/intel-pt-decoder/intel-pt-insn-decoder.h
>  create mode 100644 tools/perf/util/intel-pt-decoder/intel-pt-log.c
>  create mode 100644 tools/perf/util/intel-pt-decoder/intel-pt-log.h
>  create mode 100644 tools/perf/util/intel-pt-decoder/intel-pt-pkt-decoder.c
>  create mode 100644 tools/perf/util/intel-pt-decoder/intel-pt-pkt-decoder.h
>  create mode 100644 tools/perf/util/intel-pt.c
>  create mode 100644 tools/perf/util/intel-pt.h

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.

So this was with a distro kernel, and in the hope that I'm missing some magic new 
kernel feature, I tried it the latest -tip kernel, but it still gives me the same 
failure.

So the test newbie user got stuck after wasting some time.

Me as a kernel developer could probably figure it out, but that's not the point: 
if newbies cannot discover and use our new features then it's as if they didn't 
exist, and I'm not pulling non-existent features! ;-)

Could we please improve all this?

Thanks,


	Ingo