Safepoint timeout in scimark?
vladimir.kozlov at oracle.com
Mon Jul 11 17:15:07 UTC 2016
Yes, it is known old problem with counted loops which have expensive iterations:
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:
I added your comment to it.
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
> 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-
> # 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-
> # Problematic frame:
> # V [libjvm.so+0xfb0814] PhaseIdealLoop::get_ctrl(Node*)+0x64
> Best regards, Roman
More information about the hotspot-compiler-dev