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

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Message-ID: <20180504143021.GB26151@redhat.com>
Date:   Fri, 4 May 2018 16:30:21 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Ravi Bangoria <ravi.bangoria@...ux.ibm.com>
Cc:     mhiramat@...nel.org,
        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)

Sorry Ravi, I saved the new version for review and forgot about it... I'll
try to do this on weekend.

On 05/03, Ravi Bangoria wrote:
> 
> 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.
>