<html><body><div style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000"><div><span id="zwchr" data-marker="__DIVIDER__">---- On Jun 2, 2016, at 1:29 AM, Richard Schmitt <richard.schmitt@nxp.com> wrote:<br></span></div><div data-marker="__QUOTED_TEXT__"><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;"><style><!--
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--></style><div class="WordSection1"><p class="MsoNormal"><span style="font-size:11.0pt">We are trying to use user space LTTng to perform some performance analysis of fast-path layer 3 forwarding. We have seen that with the tracepoints enabled, we experience about a 30% increase in service time.
This is spread out over two tracepoints so each one is still contributing a good amount.</span></p><p class="MsoNormal"><span style="font-size:11.0pt"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt">This fast path is fast, about 300 cycles so we are asking a lot of efficiency of the tracepoint but for comparison, we implemented a simple ring buffer. When we run with this type of capture, we only experience
a 5% increase in service time.</span></p><p class="MsoNormal"><span style="font-size:11.0pt"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt">I’m looking for pointers. We’d rather use LTTng. Are there ways to tune LTTng ust for ultra high performance requirements. Perhaps there is a way we could write directly to ust’s ring buffers, or perhaps
preallocate the buffers?</span></p></div></blockquote><div>What is the target architecture ?<br></div><div><br data-mce-bogus="1"></div><div>I'm currently working on proposing restartable sequence system call to the kernel to<br data-mce-bogus="1"></div><div>improve the speed of getcpu and remove atomic operations from the fast path<br data-mce-bogus="1"></div><div>on arm32, intel 32/64. This will be portable to other architectures too.<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>Make sure you run a kernel with sys_membarrier available, and that you have<br data-mce-bogus="1"></div><div>a recent liburcu 0.9.x. This should take care of removing memory barriers from<br data-mce-bogus="1"></div><div>the tracing fast path.<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>Thanks,<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>Mathieu<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></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"><span style="font-size:11.0pt"> </span></p><p class="MsoNormal"><span style="font-size:11.0pt">Rich</span></p></div><br>_______________________________________________<br>lttng-dev mailing list<br>lttng-dev@lists.lttng.org<br>https://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev<br></blockquote></div><div><br></div><div data-marker="__SIG_POST__">-- <br></div><div>Mathieu Desnoyers<br>EfficiOS Inc.<br>http://www.efficios.com</div></div></body></html>