<html><body><div style="font-family: arial, helvetica, sans-serif; font-size: 12pt; color: #000000"><div><br></div><span id="zwchr" data-marker="__DIVIDER__">----- On Dec 18, 2015, at 5:02 AM, 陈志文 <zwchen@aimlab.org> wrote:<br></span><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;"><div dir="ltr">Hi, I'm a Ph.D from Hunan University of China. Recently, our group are tending to analysis concurrent hash tables using different synchronization mechanisms, urcu-based hashing is one of our targets. Today, we running an urcu-based hash table with only ten percent update operations. We found its CPU utilization is only 3% (while in a read-only workload, the CPU utilization is 50%). Is there any writer performance limits for urcu? Or why this happened in your eye?<br><div>There is our platform information: Intel SandyBridge EP with 2 sockets, each sockets with 8 cores and 2 physical threads for each core. OS: Ubuntu 14.04 LTS.</div><div>Experimental configuration: 16 threads, ten percent of update operations and 1 million initial elements in hash table.</div></div></blockquote><div><br></div><div>Are you invoking "synchronize_rcu()" after each removal from the hash table directly<br data-mce-bogus="1"></div><div>from your updater thread ? This would very likely explain a low CPU utilization.<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>I would recommend using the call_rcu() mechanism to batch those synchronize_rcu()<br data-mce-bogus="1"></div><div>calls if you don't use it already.<br data-mce-bogus="1"></div><div><br data-mce-bogus="1"></div><div>If it's not your situation, then emailing us a copy of your test code would likely help us</div><div>pinpoint the slowdown cause.<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><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 dir="ltr"><br><div>We are looking forward for your reply.</div><br><div>Thanks! <br clear="all"><br>-- <br><div class="gmail_signature"><div dir="ltr">aimlab zwchen</div></div></div></div><br>_______________________________________________<br>lttng-dev mailing list<br>lttng-dev@lists.lttng.org<br>http://lists.lttng.org/cgi-bin/mailman/listinfo/lttng-dev<br></blockquote></div><br><div data-marker="__SIG_POST__">-- <br></div><div>Mathieu Desnoyers<br>EfficiOS Inc.<br>http://www.efficios.com</div></div></body></html>