Safepoint timeout in scimark?

[Vladimir Kozlov]

Hi, Roman

Yes, it is known old problem with counted loops which have expensive iterations:

https://bugs.openjdk.java.net/browse/JDK-5014723

But we most likely will not fix it.
Instead we implemented UseCountedLoopSafepoints flag to solve rare cases when customers hit this problem.

You may hit next bug with UseCountedLoopSafepoints flag:

https://bugs.openjdk.java.net/browse/JDK-8160287

I added your comment to it.

Regards,
Vladimir

On 7/11/16 9:53 AM, Roman Kennke wrote:
> I noticed that it sometimes takes up to 20 seconds to reach a safepoint
> when running the scimark benchmark of SPECjvm2008.
>
> It looks to me like scimark is just triple nested loops with finite
> bounds, which translates to a CountedLoop, and safepoints are removed
> unconditionally from counted loops if no outer loops needs them (which
> doesn't seem to be the case). Therefore, a Java thread inside such a
> loop can only reach a safepoint when it exits the outermost loop, and
> this can take a while.
>
> This seems like a rather serious bug to me. This prevents GC from
> kicking in, deoptimizations, biased locking and probably some other
> things from responding in a timely manner. Even just killing the app
> with CTRL+C seems to be affected.
>
> Is this a known issue? Any ideas how a proper fix looks like?
>
> It can be reproduced with SPECjvm2008 like this:
>
> java -XX:+SafepointTimeout -jar SPECjvm2008.jar -ict -ikv scimark
>
> (If you have a very fast machine, you probably have to pass
> -XX:SafepointTimeoutDelay with a value lower than 10000, I think
> 10seconds is much too generous anyway)
>
>
> BTW, I tried -XX:+UseCountedLoopSafepoints, and it does indeed solve
> the problem, but ran into other problems in SPECjvm2008's compiler
> benchmarks:
>
> java -XX:+UseCountedLoopSafepoints -XX:+SafepointTimeout
> -XX:SafepointTimeoutDelay=2000 -jar SPECjvm2008.jar -ict -ikv compiler
>
> .. fails with:
>
> #
> # A fatal error has been detected by the Java Runtime Environment:
> #
> #  SIGSEGV (0xb) at pc=0x00007f7adff09814, pid=23268, tid=23296
> #
> # JRE version: OpenJDK Runtime Environment (9.0) (fastdebug build 9-
> internal+0-2016-07-11-184003.rkennke.jdk9)
> # Java VM: OpenJDK 64-Bit Server VM (fastdebug 9-internal+0-2016-07-11-
> 184003.rkennke.jdk9, mixed mode, tiered, compressed oops, g1 gc, linux-
> amd64)
> # Problematic frame:
> # V  [libjvm.so+0xfb0814]  PhaseIdealLoop::get_ctrl(Node*)+0x64
>
>
>
> Best regards, Roman
>