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

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Date:   Tue, 24 Jan 2017 14:06:22 +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>,
        Hemant Kumar <hemant@...ux.vnet.ibm.com>
Subject: Re: [PATCH v5 0/2] perf probe: add sdt probes arguments into the
 uprobe cmd string



On Tuesday 24 January 2017 01:52 PM, Ingo Molnar wrote:
> * Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com> wrote:
>
>>
>> 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,
>
> Well, I was mainly complaining about the misleading messages and flow of the 
> tooling here. Could you please improve the messages so that if I use it like the 
> way I reported it results in me trying the right approach?

Right, message is misleading. Will prepare a patch for this.

Also it's little odd flow for sdt markers, to put a probe first and then
record it while other events can be recorded directly. There was a
patch by Hemant about directly recording SDT marker events. I
don't see any updates on that:

https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1138183.html

-Ravi

> Thanks,
>
> 	Ingo
>