linux-kernel - Re: [PATCH v3 0/9] trace_uprobe: Support SDT markers having reference count (semaphore)

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Date:   Thu, 3 May 2018 14:02:00 +0530
From:   Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
To:     mhiramat@...nel.org, oleg@...hat.com
Cc:     Ravi Bangoria <ravi.bangoria@...ux.vnet.ibm.com>,
        peterz@...radead.org, srikar@...ux.vnet.ibm.com,
        rostedt@...dmis.org, acme@...nel.org, ananth@...ux.vnet.ibm.com,
        akpm@...ux-foundation.org, alexander.shishkin@...ux.intel.com,
        alexis.berlemont@...il.com, corbet@....net,
        dan.j.williams@...el.com, jolsa@...hat.com, kan.liang@...el.com,
        kjlx@...pleofstupid.com, kstewart@...uxfoundation.org,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, milian.wolff@...b.com, mingo@...hat.com,
        namhyung@...nel.org, naveen.n.rao@...ux.vnet.ibm.com,
        pc@...ibm.com, tglx@...utronix.de, yao.jin@...ux.intel.com,
        fengguang.wu@...el.com, jglisse@...hat.com
Subject: Re: [PATCH v3 0/9] trace_uprobe: Support SDT markers having reference
 count (semaphore)


On 04/17/2018 10:02 AM, Ravi Bangoria wrote:
> Userspace Statically Defined Tracepoints[1] are dtrace style markers
> inside userspace applications. Applications like PostgreSQL, MySQL,
> Pthread, Perl, Python, Java, Ruby, Node.js, libvirt, QEMU, glib etc
> have these markers embedded in them. These markers are added by developer
> at important places in the code. Each marker source expands to a single
> nop instruction in the compiled code but there may be additional
> overhead for computing the marker arguments which expands to couple of
> instructions. In case the overhead is more, execution of it can be
> omitted by runtime if() condition when no one is tracing on the marker:
>
>     if (reference_counter > 0) {
>         Execute marker instructions;
>     }   
>
> Default value of reference counter is 0. Tracer has to increment the 
> reference counter before tracing on a marker and decrement it when
> done with the tracing.

Hi Oleg, Masami,

Can you please review this :) ?

Thanks.