<div>Hello Lohit,</div><div><br></div><div>You might be interested in reading the following threads first:</div><div><br></div><div>1.</div><div><a href="http://mail.openjdk.java.net/pipermail/hotspot-gc-use/2012-March/001090.html">http://mail.openjdk.java.net/pipermail/hotspot-gc-use/2012-March/001090.html</a></div>
<div><br></div><div>2.</div><div><a href="http://mail.openjdk.java.net/pipermail/hotspot-gc-use/2012-April/001150.html">http://mail.openjdk.java.net/pipermail/hotspot-gc-use/2012-April/001150.html</a></div><div><a href="http://mail.openjdk.java.net/pipermail/hotspot-gc-use/2012-April/001153.html">http://mail.openjdk.java.net/pipermail/hotspot-gc-use/2012-April/001153.html</a></div>
<div><br></div><div>3.</div><div><a href="http://mail.openjdk.java.net/pipermail/hotspot-gc-use/2012-November/001412.html">http://mail.openjdk.java.net/pipermail/hotspot-gc-use/2012-November/001412.html</a></div><div><br>
</div><div>The comments in source code can help you get the context of what's going on:</div><div>line 688, <a href="http://hg.openjdk.java.net/jdk6/jdk6/hotspot/file/cd74fab0a5e3/src/share/vm/gc_implementation/parallelScavenge/psParallelCompact.hpp">http://hg.openjdk.java.net/jdk6/jdk6/hotspot/file/cd74fab0a5e3/src/share/vm/gc_implementation/parallelScavenge/psParallelCompact.hpp</a></div>
<div>(the link above is code from OpenJDK6's HotSpot VM, which should roughly match with your JDK6u24)</div><div><br></div><div>Hope it helps,</div><div>Kris</div><br><div class="gmail_quote">On Mon, Nov 5, 2012 at 1:54 AM, lohit <span dir="ltr"><<a href="mailto:lohit.vijayarenu@gmail.com" target="_blank">lohit.vijayarenu@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">Hello Devs,<div><br></div><div>We are trying to profile Full GC performance on our Java server. </div><div>Heap Size is about 80G, running on CentOS 5.5. As of now we use ParallelOldGC for old generation compactions. </div>
<div>When we trigger fullGC by hand we see that it takes more than 2 minutes. </div><div>Running mpstat showed that for about half of the time only one CPU was spinning 100% and all others were idle. (Box has 24 CPUs)</div>
<div>While this was happening we took stack trace and see that all threads are waiting behind one thread whose trace look like below.</div><div><br></div><div>Question is the below expected. Even though documentation says parallelOldGC uses multiple threads, are there cases when this kind of serialization happens where all threads wait behind single thread.</div>
<div>I might have given very little information about problem, but let me know if I could add any more information to know about this</div><div><br></div><div><pre style="margin-top:0px;margin-bottom:0px;padding:0px;font-size:13px;line-height:1.3em;max-height:30em;overflow:auto;word-wrap:normal">
Thread 18 (Thread 0x419f2940 (LWP 55314)):^M
#0 0x00007f051735e3e0 in BitMap::get_next_one_offset_inline_aligned_right(unsigned long, unsigned long) const ()^M
from /usr/java/jdk1.6.0_24/jre/lib/amd64/server/libjvm.so^M
#1 0x00007f051735e09e in ParMarkBitMap::live_words_in_range(HeapWord*, oopDesc*) const ()^M
from /usr/java/jdk1.6.0_24/jre/lib/amd64/server/libjvm.so^M
#2 0x00007f0517398848 in ParallelCompactData::calc_new_pointer(HeapWord*) ()^M
from /usr/java/jdk1.6.0_24/jre/lib/amd64/server/libjvm.so^M
#3 0x00007f05173413ec in objArrayKlass::oop_update_pointers(ParCompactionManager*, oopDesc*) ()^M
from /usr/java/jdk1.6.0_24/jre/lib/amd64/server/libjvm.so^M
#4 0x00007f051739d0a7 in PSParallelCompact::update_deferred_objects(ParCompactionManager*, PSParallelCompact::SpaceId) ()^M
from /usr/java/jdk1.6.0_24/jre/lib/amd64/server/libjvm.so^M
#5 0x00007f051739c6c7 in PSParallelCompact::compact() () from /usr/java/jdk1.6.0_24/jre/lib/amd64/server/libjvm.so^M
#6 0x00007f051739aeca in PSParallelCompact::invoke_no_policy(bool) ()^M
from /usr/java/jdk1.6.0_24/jre/lib/amd64/server/libjvm.so^M
#7 0x00007f051739a845 in PSParallelCompact::invoke(bool) () from /usr/java/jdk1.6.0_24/jre/lib/amd64/server/libjvm.so^M
#8 0x00007f05174a0bb0 in VM_ParallelGCSystemGC::doit() () from /usr/java/jdk1.6.0_24/jre/lib/amd64/server/libjvm.so^M
#9 0x00007f05174ada5a in VM_Operation::evaluate() () from /usr/java/jdk1.6.0_24/jre/lib/amd64/server/libjvm.so^M
(More stack frames follow...)^M</pre><span class="HOEnZb"><font color="#888888"><div><br></div>-- <br>Have a Nice Day!<br>Lohit<br>
</font></span></div>
</blockquote></div><br>