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

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Message-Id: <20180228120617.GA63063@linux.vnet.ibm.com>
Date:   Wed, 28 Feb 2018 04:06:17 -0800
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:     Ravi Bangoria <ravi.bangoria@...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
Subject: Re: [RFC 0/4] trace_uprobe: Support SDT markers having semaphore

* 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?