Hi Akara, thanks for all the detailed information, I am 95% certain that I know what happens—and I’d call it a bug. To the casual observer the code in DirectByteBufferPool looks like a CAS loop, but it actually is an open-coded primitive spinlock. If you have more threads competing for this lock than you have CPUs it might well happen that the kernel decides to schedule out a thread that was holding this lock, and since it is not a normal, honest lock, the kernel has no idea why the other threads now all are spinning like mad. It probably takes some server-type hardware and a bit of patience and good monitoring to actually notice, which is why you are the first person to report it :-)
I created a ticket <https://github.com/akka/akka/issues/17216> to track this. Regards, Roland > 17 apr 2015 kl. 05:20 skrev Akara Sucharitakul <akara.sucharita...@gmail.com>: > > Nope, this is actually Ubuntu 10.10 on a 4vCPU VM (likely ESX but I can't > tell for sure). Couple more pieces of information: > Further experiments with parallelism-factor lowered to 1.0 no longer shows > the spikes. > Trying to profile the spikes with JMC would cause the spikes not to happen. > The sampling somehow changed the timing characteristics. > Switching the ForkJoinExecutor to Java8, the initial experiments show similar > spikes. Since this was quick implementation of ExecutorServiceConfigurator to > get Java 8 ForkJoinPool to work, there is still a bit of refinement we need > to do before we can conclude on this fact. > I'll keep updating this thread as we find out more. Expect it to be a long > process, though. > > Thanks! > -Akara > > On Thursday, April 16, 2015 at 5:03:48 AM UTC-7, Martynas Mickevičius wrote: > Hi, > > are you running this application on Windows? There is a known situation > <https://github.com/akka/akka/issues/16942> where high CPU usage might occur > when using TCP with akka IO. > > On Tue, Apr 14, 2015 at 7:28 AM, Akara Sucharitakul <akara.suc...@gmail.com > <javascript:>> wrote: > Scala 2.11.6, Akka 2.3.9, Spray 1.3.2. > > When testing a particular workload, we ran into CPU spikes. The avg CPU load > is less than 5% but about 6-7 minutes into the run, we start to see CPU > spiking to near 100% lasting for several seconds. This repeats itself every > 6-7 minutes. We can't correlate this with a particular GC activity just yet. > We tested against Java 7_45 but tried Java 8 without much change. > > Spray is configured on the default-dispatcher (Spray default). > > Trying to capture thread dumps at the time spikes happening reveal 9 threads > spinning on the followings: > > "default-akka.actor.default-dispatcher-11" prio=10 tid=0x0000000001b2b800 > nid=0x3752 runnable [0x00007f1191d40000] > java.lang.Thread.State: RUNNABLE > at > akka.io.DirectByteBufferPool.takeBufferFromPool(DirectByteBufferPool.scala:41) > at akka.io.DirectByteBufferPool.acquire(DirectByteBufferPool.scala:31) > at akka.io.TcpConnection.doRead(TcpConnection.scala:231) > at > akka.io.TcpConnection$$anonfun$connected$1.applyOrElse(TcpConnection.scala:87) > at scala.PartialFunction$OrElse.applyOrElse(PartialFunction.scala:171) > at akka.actor.Actor$class.aroundReceive(Actor.scala:465) > at akka.io.TcpConnection.aroundReceive(TcpConnection.scala:28) > at akka.actor.ActorCell.receiveMessage(ActorCell.scala:516) > at akka.actor.ActorCell.invoke(ActorCell.scala:487) > at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:254) > at akka.dispatch.Mailbox.run(Mailbox.scala:221) > at akka.dispatch.Mailbox.exec(Mailbox.scala:231) > at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260) > at > scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339) > at > scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979) > at > scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107) > > 2 threads show this spinning: > > "default-akka.actor.default-dispatcher-8" prio=10 tid=0x0000000001d6f000 > nid=0x374f runnable [0x00007f11928d2000] > java.lang.Thread.State: RUNNABLE > at > akka.io.DirectByteBufferPool.offerBufferToPool(DirectByteBufferPool.scala:66) > at akka.io.DirectByteBufferPool.release(DirectByteBufferPool.scala:34) > at akka.io.TcpConnection.doRead(TcpConnection.scala:245) > at > akka.io.TcpConnection$$anonfun$connected$1.applyOrElse(TcpConnection.scala:87) > at scala.PartialFunction$OrElse.applyOrElse(PartialFunction.scala:171) > at akka.actor.Actor$class.aroundReceive(Actor.scala:465) > at akka.io.TcpConnection.aroundReceive(TcpConnection.scala:28) > at akka.actor.ActorCell.receiveMessage(ActorCell.scala:516) > at akka.actor.ActorCell.invoke(ActorCell.scala:487) > at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:254) > at akka.dispatch.Mailbox.run(Mailbox.scala:221) > at akka.dispatch.Mailbox.exec(Mailbox.scala:231) > at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260) > at > scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339) > at > scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979) > at > scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107) > > 1 thread is on I/O: > > "default-akka.actor.default-dispatcher-4" prio=10 tid=0x0000000001be2800 > nid=0x36ff runnable [0x00007f11924b0000] > java.lang.Thread.State: RUNNABLE > at sun.nio.ch.SocketChannelImpl.read(SocketChannelImpl.java:295) > - locked <0x00000007d3b7e940> (a java.lang.Object) > at akka.io.TcpConnection.innerRead$1(TcpConnection.scala:216) > at akka.io.TcpConnection.doRead(TcpConnection.scala:232) > at > akka.io.TcpConnection$$anonfun$connected$1.applyOrElse(TcpConnection.scala:87) > at scala.PartialFunction$OrElse.applyOrElse(PartialFunction.scala:171) > at akka.actor.Actor$class.aroundReceive(Actor.scala:465) > at akka.io.TcpConnection.aroundReceive(TcpConnection.scala:28) > at akka.actor.ActorCell.receiveMessage(ActorCell.scala:516) > at akka.actor.ActorCell.invoke(ActorCell.scala:487) > at akka.dispatch.Mailbox.processMailbox(Mailbox.scala:254) > at akka.dispatch.Mailbox.run(Mailbox.scala:221) > at akka.dispatch.Mailbox.exec(Mailbox.scala:231) > at scala.concurrent.forkjoin.ForkJoinTask.doExec(ForkJoinTask.java:260) > at > scala.concurrent.forkjoin.ForkJoinPool$WorkQueue.runTask(ForkJoinPool.java:1339) > at > scala.concurrent.forkjoin.ForkJoinPool.runWorker(ForkJoinPool.java:1979) > at > scala.concurrent.forkjoin.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:107) > > All in all, during this time there is no app logic being executed on the > default dispatcher at all (12 threads on the default-dispatcher). > > For reference, here's the takeBufferFromPool implementation: > > @tailrec > private final def takeBufferFromPool(): ByteBuffer = > if (locked.compareAndSet(false, true)) { > val buffer = > try if (buffersInPool > 0) { > buffersInPool -= 1 > pool(buffersInPool) > } else null > finally locked.set(false) > > // allocate new and clear outside the lock > if (buffer == null) > allocate(defaultBufferSize) > else { > buffer.clear() > buffer > } > } else takeBufferFromPool() // spin while locked > > It seems like some thread is holding locked (AtomicBoolean) to true causing > the other threads to spin, but I do not seem to find the offending code. > > Now to the set of questions: > Using thread-pool-executor instead of fork-join-executor prevents the spikes > from happening. Anybody running into similar issues with fork-join-executor? > Any know bug in the Scala ForkJoinPool? > I don't seem to find a way to use the Java 8 or Java 7 ForkJoinPool directly > in the Akka docs. Is there a way I can test it out? > Any other thoughts? > Thanks in advance! > -Akara > > > > -- > >>>>>>>>>> Read the docs: http://akka.io/docs/ <http://akka.io/docs/> > >>>>>>>>>> Check the FAQ: > >>>>>>>>>> http://doc.akka.io/docs/akka/current/additional/faq.html > >>>>>>>>>> <http://doc.akka.io/docs/akka/current/additional/faq.html> > >>>>>>>>>> Search the archives: https://groups.google.com/group/akka-user > >>>>>>>>>> <https://groups.google.com/group/akka-user> > --- > You received this message because you are subscribed to the Google Groups > "Akka User List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to akka-user+...@googlegroups.com <javascript:>. > To post to this group, send email to akka...@googlegroups.com <javascript:>. > Visit this group at http://groups.google.com/group/akka-user > <http://groups.google.com/group/akka-user>. > For more options, visit https://groups.google.com/d/optout > <https://groups.google.com/d/optout>. > > > > -- > Martynas Mickevičius > Typesafe <http://typesafe.com/> – Reactive > <http://www.reactivemanifesto.org/> Apps on the JVM > > -- > >>>>>>>>>> Read the docs: http://akka.io/docs/ <http://akka.io/docs/> > >>>>>>>>>> Check the FAQ: > >>>>>>>>>> http://doc.akka.io/docs/akka/current/additional/faq.html > >>>>>>>>>> <http://doc.akka.io/docs/akka/current/additional/faq.html> > >>>>>>>>>> Search the archives: https://groups.google.com/group/akka-user > >>>>>>>>>> <https://groups.google.com/group/akka-user> > --- > You received this message because you are subscribed to the Google Groups > "Akka User List" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to akka-user+unsubscr...@googlegroups.com > <mailto:akka-user+unsubscr...@googlegroups.com>. > To post to this group, send email to akka-user@googlegroups.com > <mailto:akka-user@googlegroups.com>. > Visit this group at http://groups.google.com/group/akka-user > <http://groups.google.com/group/akka-user>. > For more options, visit https://groups.google.com/d/optout > <https://groups.google.com/d/optout>. Dr. Roland Kuhn Akka Tech Lead Typesafe <http://typesafe.com/> – Reactive apps on the JVM. twitter: @rolandkuhn <http://twitter.com/#!/rolandkuhn> -- >>>>>>>>>> Read the docs: http://akka.io/docs/ >>>>>>>>>> Check the FAQ: >>>>>>>>>> http://doc.akka.io/docs/akka/current/additional/faq.html >>>>>>>>>> Search the archives: https://groups.google.com/group/akka-user --- You received this message because you are subscribed to the Google Groups "Akka User List" group. To unsubscribe from this group and stop receiving emails from it, send an email to akka-user+unsubscr...@googlegroups.com. To post to this group, send email to akka-user@googlegroups.com. Visit this group at http://groups.google.com/group/akka-user. For more options, visit https://groups.google.com/d/optout.
