<html><body><div style="font-family: times new roman, new york, times, serif; font-size: 12pt; color: #000000"><hr id="zwchr"><blockquote style="border-left:2px solid #1010FF;margin-left:5px;padding-left:5px;color:#000;font-weight:normal;font-style:normal;text-decoration:none;font-family:Helvetica,Arial,sans-serif;font-size:12pt;"><b>From: </b>"Máté Ferenczy" <mate.ferenczy@ericsson.com><br><b>To: </b>"mathieu desnoyers" <mathieu.desnoyers@efficios.com><br><b>Cc: </b>lttng-dev@lists.lttng.org<br><b>Sent: </b>Wednesday, December 11, 2013 6:52:22 PM<br><b>Subject: </b>RE: efficient use of LTTng in legacy codebase<br><div><br></div><style><!--
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--></style><div class="WordSection1"><p class="MsoNormal">I found this email thread: <a href="https://www.mail-archive.com/lttng-dev@lists.lttng.org/msg02278.html" target="_blank">
https://www.mail-archive.com/lttng-dev@lists.lttng.org/msg02278.html</a><br data-mce-bogus="1"></p><p class="MsoNormal">According to this I could just check caa_unlikely(__tracepoint_##provider##___##name.state). However, Dave claims that this state will stay true even if the tracepoint is disabled. Is there anything else I should check for?</p></div></blockquote><div><br></div><div>I would recommend doing this in the UST probe provider instead. Within the TRACEPOINT_EVENT "TP_FIELD" section, when you declare your string field, you could parse the format string there in the last argument of a ctf_string() (a statement expression). The format string would be received as parameter by the tracepoint, along with a variable arg list (...). In the probe, it would be turned into a va_list (see stdarg(3)), and the parameters could be decoded into a string there. This has the benefit of moving the serialization call out-of-line into the probe provider rather than clobbering the tracepoint call site.<br></div><div><br></div><div>Thoughts ?<br></div><div><br></div><div>Thanks,<br></div><div><br></div><div>Mathieu<br></div><div><br></div><blockquote style="border-left:2px solid #1010FF;margin-left:5px;padding-left:5px;color:#000;font-weight:normal;font-style:normal;text-decoration:none;font-family:Helvetica,Arial,sans-serif;font-size:12pt;"><div class="WordSection1"><p class="MsoNormal">Thanks,</p><p class="MsoNormal">Mate</p><p class="MsoNormal"><span style="color:#1F497D"> </span></p><div><div style="border:none;border-top:solid #B5C4DF 1.0pt;padding:3.0pt 0in 0in 0in"><p class="MsoNormal"><b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif"">From:</span></b><span style="font-size:10.0pt;font-family:"Tahoma","sans-serif""> Máté Ferenczy
<br>
<b>Sent:</b> Wednesday, December 11, 2013 12:17 PM<br>
<b>To:</b> 'mathieu.desnoyers@efficios.com'<br>
<b>Cc:</b> 'lttng-dev@lists.lttng.org'<br>
<b>Subject:</b> efficient use of LTTng in legacy codebase</span></p></div></div><p class="MsoNormal">Hello Mathieu,</p><p class="MsoNormal">Our team was asked to support LTTng UST solution in a legacy codebase. The existing codebase is fairly large, and the requirement is that we provide all the existing logs and debugs in the system as LTTng traces.</p><p class="MsoNormal">The planned solution so far was just to pass everything we have as text (strings) to LTTng. For that we obviously have to convert the printf-like format string and parameter list to a string by calling snprintf before giving the string
to the LTTng API. That would however mean, that these snprintfs are getting called every time even if there is no listener/active trace session for the given trace. In this case, all those unnecessary snprintf calls may end up significantly impacting the performance
of our applications.</p><p class="MsoNormal">In order to work around this, we were thinking that if there was a way to query the LTTng library from our application code whether there is an active tracing session for the given trace level, we could avoid calling those snprintfs in
case they are not needed. Do you think it would be feasible to easily get this data from LTTng lib? If yes, can you provide us some pointers where to look at in order to do those changes ourselves?</p><p class="MsoNormal">Any suggestions are welcome.</p><p class="MsoNormal">Thank you,</p><p class="MsoNormal">Mate Ferenczy</p></div></blockquote><div><br><br></div><div><br></div><div>-- <br></div><div><span name="x"></span>Mathieu Desnoyers<br>EfficiOS Inc.<br>http://www.efficios.com<span name="x"></span><br></div></div></body></html>