[jvm-l] slow downs in invokedynamic native code

[Remi Forax]

The symptoms are really like a deoptimization storm, 
setCallSiteTargetNormal goes to a safepoint (which is worst that only having the compiler/JIT lock because all threads are stopped), 
when either a code calls setTarget or a SwithPoint is invalidated. 

You have a deopt storm when the JIT compiles a code that contains a callsite that is always invalid, so the VM enters in loop like this, 
JIT compile a blob 
execute the blob 
deopt 
jump back in the interpreter 
rinse and repeat 

The root cause is a bug in the invalidation logic of the language runtime (not the VM) but it's hard to spot without a reproducible test case because 
when the JIT compiles a blob of codes there are several callsites inside that blob and usually only one is the faulty one. 

We already have discussed about that point several times, 
John is a proponent of marking the callsite has should never be optimized again, 
which at least stop the storm issue but it sweeps the real cause of the bug under carpet, 
I would prefer, consider these kind of bugs as a language runtime bugs that should be investigated by the runtime developers. 

Perhaps a middle ground is to mark the callsite as not compilable anymore *and* emit a warning (like when the code cache is full) to not hide the root cause of the bug. 

Rémi 

----- Mail original -----

> De: "Hannes Wallnöfer" <hannesw at gmail.com>
> À: jvm-languages at googlegroups.com
> Envoyé: Mercredi 16 Mars 2016 11:52:42
> Objet: Re: [jvm-l] slow downs in invokedynamic native code

> I've filed a bug for this:

> https://bugs.openjdk.java.net/browse/JDK-8151981

> For the Nashorn report, the only thing we know is that it involves pretty
> large scripts that are being re-evaluated in new ScriptEngines, with 8
> engines at a time. So it seems quite possible that some implementation
> detail is stressed beyond the point where it performs efficiently.

> Hannes

> 2016-03-16 11:44 GMT+01:00 Duncan MacGregor < duncan.macgregor at gmail.com > :

> > I haven't seen this, but setCallSiteTargetNormal does have to get the
> > compiler lock, so contention can definitely cause problems. Is there a
> > chance you're repeatedly invalidating and setting targets? Or generating
> > lots of new mutable call sites?
> 

> > The other possibility is that the data structures that store the target
> > information aren't scaling, but j have seen a big problem there before, and
> > Magik on Java apps tend to be large, so I'd expect to have hit any problems
> > by now.
> 

> > Duncan.
> 

> > On 16 Mar 2016, at 10:28, Hannes Wallnöfer < hannesw at gmail.com > wrote:
> 

> > > Hi Jochen,
> > 
> 

> > > we recently had a report on nashorn-dev that could be related. A user is
> > > re-evaluating the same or similar code again and seeing more than 20x
> > > slowdown compared to the fist evaluation.
> > 
> 

> > > http://mail.openjdk.java.net/pipermail/nashorn-dev/2016-March/006024.html
> > 
> 

> > > The thing is that he is using fresh ScriptEngines for the second
> > > evaluation,
> > > so the Nashorn engines should not share anything. As with your case,
> > > Jvisualvm shows that 80% of time is spent in
> > > java.lang.invoke.MethodHandleNatives.setCallSiteTargetNormal().
> > 
> 

> > > Hannes
> > 
> 

> > > 2016-03-15 10:28 GMT+01:00 Jochen Theodorou < blackdrag at gmx.org > :
> > 
> 

> > > > Hi,
> > > 
> > 
> 

> > > > One of our users has a web application using Groovy with indy activated
> > > > and
> > > > describes the following problem:
> > > 
> > 
> 

> > > > > At random intervals and a random times our web servers will go from
> > > > > serving
> > > > > responses in the 300 ms range to taking 30 seconds or more. Sometimes
> > > > > the
> > > > > servers will recover, sometimes they require a restart of the
> > > > > webserver
> > > > > (spring boot/tomcat). When the applications slow down we always see
> > > > > the
> > > > > tomcat thread pool hit the maximum size. Every single thread in the
> > > > > thread
> > > > > pool is in the RUNNABLE state but appears to be making no progress.
> > > > > Successive thread dumps show that the stacks are changing, but VERY
> > > > > slowly.
> > > > > The top of the stack is always this method:
> > > > 
> > > 
> > 
> 

> > > > > at
> > > > > java.lang.invoke.MethodHandleNatives.setCallSiteTargetNormal(Native
> > > > > Method).
> > > > 
> > > 
> > 
> 

> > > > > The other common condition is that whatever application code is on
> > > > > the
> > > > > stack
> > > > > is always dynamically compiled. Code that is @CompileStatic is NEVER
> > > > > on
> > > > > the
> > > > > stack when we see these slowdowns.
> > > > 
> > > 
> > 
> 

> > > > > The thread dumps showed that the application code is never waiting on
> > > > > locks,
> > > > > socket reads, db connections, etc.
> > > > 
> > > 
> > 
> 

> > > > Mabye worth mentioning, that with @CompileStatic annotated code is not
> > > > using
> > > > invokedynamic....
> > > 
> > 
> 

> > > > Anyway... I am wondering if anyone has had something like this before.
> > > > My
> > > > first reaction to this description would be a bug in the JVM... or a
> > > > performance bottleneck in the JVM.... but to spend literally seconds in
> > > > native code is pretty bad in any case. On the other hand I am not
> > > > having
> > > > this web application here to experiment with. The only part I did hear
> > > > is,
> > > > that removing the indy version of Groovy seems to fix the problem. So
> > > > it
> > > > must be either our use of indy, or indy itself having a problem here.
> > > > But
> > > > asides from this conclusion I am quite at a loss.
> > > 
> > 
> 

> > > > Question 1: Did anyone have a similar problem before?
> > > 
> > 
> 
> > > > Question 2: Maybe more to the JVM engineers, is it even possible for
> > > > the
> > > > indy
> > > > part to suddenly tak seconds on compilation - or especially the
> > > > mentioned
> > > > native method?
> > > 
> > 
> 

> > > > bye Jochen
> > > 
> > 
> 

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