linux-kernel - Re: [PATCH v5 0/2] perf probe: add sdt probes arguments into the uprobe cmd string

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Message-Id: <5886FB0B.40901@linux.vnet.ibm.com>
Date:   Tue, 24 Jan 2017 12:28:19 +0530
From:   Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Alexis Berlemont <alexis.berlemont@...il.com>,
        linux-kernel@...r.kernel.org, peterz@...radead.org,
        mingo@...hat.com, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, Jiri Olsa <jolsa@...hat.com>,
        Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
Subject: Re: [PATCH v5 0/2] perf probe: add sdt probes arguments into the
 uprobe cmd string



On Wednesday 14 December 2016 01:06 PM, Ingo Molnar wrote:
> * Alexis Berlemont <alexis.berlemont@...il.com> wrote:
>
>> Hi Masami,
>>
>> Many thanks for your mail.
>>
>> Here is another patch set which tries to fix the points you mentioned:
>>
>> * Skip the arguments containing a constant ($123); 
>> * Review the code in charge of the register renaming (search for '%'
>>   and parse it);
>> * Minor changes (print the argument in case of error, skipping, check
>>   the sdt arg type index);
>>
>> Many thanks,
>>
>> Alexis.
>>
>> Alexis Berlemont (2):
>>   perf sdt: add scanning of sdt probles arguments
>>   perf probe: add sdt probes arguments into the uprobe cmd string
> I'd like to hijack this thread to report an SDT oddity - one of my boxen reports 
> lots of SDT tracepoints in 'perf list':
>
>   mem:<addr>[/len][:access]                          [Hardware breakpoint]
>
>   sdt_libc:lll_lock_wait_private                     [SDT event]
>   sdt_libc:longjmp                                   [SDT event]
>   sdt_libc:longjmp_target                            [SDT event]
>   sdt_libc:memory_arena_new                          [SDT event]
>   sdt_libc:memory_arena_retry                        [SDT event]
>   sdt_libc:memory_arena_reuse                        [SDT event]
>   sdt_libc:memory_arena_reuse_free_list              [SDT event]
>   sdt_libc:memory_arena_reuse_wait                   [SDT event]
>   sdt_libc:memory_calloc_retry                       [SDT event]
>   sdt_libc:memory_heap_free                          [SDT event]
>   ...
>
> But none of them work:
>
>   Error:  No permissions to read /sys/kernel/debug/tracing/events/sdt_libc/longjmp
>   Hint:   Try 'sudo mount -o remount,mode=755 /sys/kernel/debug/tracing'
>
>   ...
>
>   Error:  File /sys/kernel/debug/tracing/events/sdt_libc/longjmp not found.
>   Hint:   Perhaps this kernel misses some CONFIG_ setting to enable this feature?.
>
> What kind of patches are required for SDT probes to work?

Hi Ingo,

I suppose you are trying to record SDT events without probing it.
In that case, first put a probe on an event and then try to record
it. For example,

$ ./perf list | grep sdt_
  sdt_glib:main__after_prepare                       [SDT event]
  sdt_glib:main__before_dispatch                     [SDT event]
  ...

$ ./perf record -a -e sdt_glib:main__after_prepare
  event syntax error: 'sdt_glib:main__after_prepare'
                       \___ unknown tracepoint

  Error:  File /sys/kernel/debug/tracing/events/sdt_glib/main__after_prepare not found.
  Hint: Perhaps this kernel misses some CONFIG_ setting to enable this feature?.
  ...

$ ./perf probe sdt_glib:main__after_prepare
  Added new events:
    sdt_glib:main__after_prepare (on %main__after_prepare in /usr/lib64/libglib-2.0.so.0.5000.2)
    sdt_glib:main__after_prepare_1 (on %main__after_prepare in /usr/lib64/libglib-2.0.so.0.5000.2)

  You can now use it in all perf tools, such as:

    perf record -e sdt_glib:main__after_prepare_1 -aR sleep 1

$ ./perf record -a -e sdt_glib:main__after_prepare
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.191 MB perf.data ]

-Ravi