Re: [PATCH] perf tool sort: Use default sort if evlist is empty

[David Carrillo-Cisneros]

On Fri, Jul 21, 2017 at 12:44 AM, Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
> On Thu, Jul 20, 2017 at 10:11:57PM -0700, David Carrillo-Cisneros wrote:
>> Fixes bug noted by Jiri in https://lkml.org/lkml/2017/6/13/755 and caused
>> by commit d49dadea7862 ("perf tools: Make 'trace' or 'trace_fields' sort
>>    key default for tracepoint events")
>> not taking into account that evlist is empty in pipe-mode.
>>
>> Before this commit, pipe mode will only show bogus "100.00%  N/A" instead
>> of correct output as follows:
>>
>>   $ perf record -o - sleep 1 | perf report -i -
>>   # To display the perf.data header info, please use --header/--header-only options.
>>   #
>>   [ perf record: Woken up 1 times to write data ]
>>   [ perf record: Captured and wrote 0.000 MB - ]
>>   #
>>   # Total Lost Samples: 0
>>   #
>>   # Samples: 8  of event 'cycles:ppH'
>>   # Event count (approx.): 145658
>>   #
>>   # Overhead  Trace output
>>   # ........  ............
>>   #
>>      100.00%  N/A
>>
>> Correct output, after patch:
>>
>>   $ perf record -o - sleep 1 | perf report -i -
>>   # To display the perf.data header info, please use --header/--header-only options.
>>   #
>>   [ perf record: Woken up 1 times to write data ]
>>   [ perf record: Captured and wrote 0.000 MB - ]
>>   #
>>   # Total Lost Samples: 0
>>   #
>>   # Samples: 8  of event 'cycles:ppH'
>>   # Event count (approx.): 191331
>>   #
>>   # Overhead  Command  Shared Object      Symbol
>>   # ........  .......  .................  .................................
>>   #
>>       81.63%  sleep    libc-2.19.so       [.] _exit
>>       13.58%  sleep    ld-2.19.so         [.] do_lookup_x
>>        2.34%  sleep    [kernel.kallsyms]  [k] context_switch
>>        2.34%  sleep    libc-2.19.so       [.] __GI___libc_nanosleep
>>        0.11%  perf     [kernel.kallsyms]  [k] __intel_pmu_enable_a
>>
>
> I wonder we could reinit the sortorder once we know what
> events we have in pipe, and recognize the tracepoint output
> properly:

I see this hard to do since, at any given point while traversing the
pipe's content, the best we can do is guess that we've seen all event
types. Then we'd need to fall back and redo the output whenever a new
sample refutes our last guess.

>
>         [root@krava perf]# ./perf record -e 'sched:sched_switch' sleep 1 |  ./perf report
>         # To display the perf.data header info, please use --header/--header-only options.
>
>         SNIP
>
>         #
>         # Overhead  Command  Shared Object      Symbol
>         # ........  .......  .................  ..............
>         #
>            100.00%  sleep    [kernel.kallsyms]  [k] __schedule
>
>
> also I've got another crash for (added -a option for above example):
>
>         [root@krava perf]# ./perf record -e 'sched:sched_switch' -a sleep 1 |  ./perf report
>         # To display the perf.data header info, please use --header/--header-only options.
>         #
>         [ perf record: Woken up 1 times to write data ]
>         [ perf record: Captured and wrote 0.000 MB (null) ]
>         Segmentation fault (core dumped)
>
> catchsegv got:
>         /home/jolsa/kernel/linux-perf/tools/perf/util/ordered-events.c:85(free_dup_event)[0x51a6a5]
>         ./perf(ordered_events__free+0x5c)[0x51b0b7]
>         /home/jolsa/kernel/linux-perf/tools/perf/util/session.c:1751(__perf_session__process_pipe_events)[0x518abb]
>         ./perf(perf_session__process_events+0x91)[0x5190f0]
>         /home/jolsa/kernel/linux-perf/tools/perf/builtin-report.c:598(__cmd_report)[0x443a91]
>         ./perf(cmd_report+0x169b)[0x4455a3]
>         /home/jolsa/kernel/linux-perf/tools/perf/perf.c:296(run_builtin)[0x4be1b0]
>         /home/jolsa/kernel/linux-perf/tools/perf/perf.c:348(handle_internal_command)[0x4be41d]
>         /home/jolsa/kernel/linux-perf/tools/perf/perf.c:395(run_argv)[0x4be56f]
>         ./perf(main+0x2d6)[0x4be949]
>         /lib64/libc.so.6(__libc_start_main+0xf1)[0x7f3de8a10401]
>         ./perf(_start+0x2a)[0x42831a]
>
> looks like some mem corruption.. will try to follow up
> on this later if nobody beats me to it ;-)

Cannot reproduce it in acme's perf/core building the tool with
  make NO_LIBPYTHON=1 LDFLAGS=-static

If you have a file with the perf record output causing perf report's
crash, I'd like to take a look.

Thanks,
David