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

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Date:   Thu, 1 Mar 2018 10:40:43 +0530
From:   Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
To:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
Cc:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        alexander.shishkin@...ux.intel.com, jolsa@...hat.com,
        namhyung@...nel.org, linux-kernel@...r.kernel.org,
        rostedt@...dmis.org, mhiramat@...nel.org,
        ananth@...ux.vnet.ibm.com, naveen.n.rao@...ux.vnet.ibm.com,
        oleg@...hat.com, Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>
Subject: Re: [RFC 0/4] trace_uprobe: Support SDT markers having semaphore



On 02/28/2018 05:36 PM, Srikar Dronamraju wrote:
> * Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com> [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