linux-kernel - Re: [PATCH v5 10/10] perf probe: Support SDT markers having reference counter (semaphore)

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Date:   Tue, 3 Jul 2018 13:30:01 +0530
From:   Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
To:     Srikar Dronamraju <srikar@...ux.vnet.ibm.com>, mhiramat@...nel.org
Cc:     oleg@...hat.com, rostedt@...dmis.org, 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, corbet@....net,
        linux-doc@...r.kernel.org, ananth@...ux.vnet.ibm.com,
        alexis.berlemont@...il.com, naveen.n.rao@...ux.vnet.ibm.com,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...ux-mips.org,
        linux@...linux.org.uk, ralf@...ux-mips.org, paul.burton@...s.com,
        Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Subject: Re: [PATCH v5 10/10] perf probe: Support SDT markers having reference
 counter (semaphore)

Hi Srikar,

On 07/02/2018 08:27 PM, Srikar Dronamraju wrote:
> * Ravi Bangoria <ravi.bangoria@...ux.ibm.com> [2018-06-28 10:52:09]:
> 
>> With this, perf buildid-cache will save SDT markers with reference
>> counter in probe cache. Perf probe will be able to probe markers
>> having reference counter. Ex,
>>
>>   # readelf -n /tmp/tick | grep -A1 loop2
>>     Name: loop2
>>     ... Semaphore: 0x0000000010020036
>>
>>   # ./perf buildid-cache --add /tmp/tick
> 
> Would this perf buildid-cache work if the executable is stripped of
> symbols?

Description of SDT markers resides in .notes section. If .notes section
is there, binary has SDT markers, if .notes section is not there, binary
does not have any SDT markers. So SDT markers does not have anything to
do with symbol table.

> 
>>   # ./perf probe sdt_tick:loop2
>>   # ./perf stat -e sdt_tick:loop2 /tmp/tick
>>     hi: 0
>>     hi: 1
>>     hi: 2
>>     ^C
>>      Performance counter stats for '/tmp/tick':
>>                  3      sdt_tick:loop2
>>        2.561851452 seconds time elapsed
> 
> Also can we document how to use SDT markers with perf under perf-probe
> or perf-build-cache?
> 

Yes, perf-buildid-cache and perf-probe man pages describes about SDT
markers.

Thanks,
Ravi