Re: [RFC 0/4] trace_uprobe: Support SDT markers having semaphore

[Ravi Bangoria]

On 02/28/2018 05:36 PM, Srikar Dronamraju wrote:
> * Ravi Bangoria <ravi.bangoria@xxxxxxxxxxxxxxxxxx> [2018-02-28 13:23:41]:
>
>>   # readelf -n ./tick
>>   Provider: tick
>>   Name: loop2
>>   ... Semaphore: 0x0000000010020036
>>
>>   # readelf -SW ./tick | grep probes
>>   [25] .probes           PROGBITS        0000000010020034 010034
>>
>>
>> Semaphore offset is 0x10036. I don't have educated 'perf probe'
>> about semaphore. So instead of using 'perf probe' command, I'm
>> manually adding entry in the <tracefs>/uprobe_events file.
>> Special char * denotes semaphore offset.
>>
>>
>>   # echo "p:sdt_tick/loop2 /tmp/tick:0x6e4 *0x10036" > uprobe_events
>>
>>   # perf stat -e sdt_tick:loop2 -- /tmp/tick
>>   hi: 0
>>   hi: 1
>>   hi: 2
>>   hi: 3
>>   ^C
>>   Performance counter stats for '/tmp/tick':
>>               4      sdt_tick:loop2                                              
>>      3.359047827 seconds time elapsed
>>
>>
>> Feedback?
>>
>> TODO:
>>  - Educate perf tool about semaphore.
>>
> Is it possible to extend perf buildcache with a new option to work with
> semaphore?

Yes, that should be fairly easy to do. Will add a patch for that.

Thanks for the review,
Ravi