Generational ZGC crashes on specbjbb

Erik Osterlund erik.osterlund at
Mon Oct 31 09:21:18 UTC 2022

Hi Liang,

Thank you for the feedback. This was very helpful feedback. It suddenly explains so much.
I didn’t implement AVX512 arraycopy intrinsics for generational ZGC, so instead I had a hook
to bail out of conjoint and disjoint AVX512 arraycopy. Recently, the arraycopy code moved to
a new file, and it looks like only one of those too points survived a recent merge merge. We
are missing the one for conjoint AVX512 arraycopy. Whe run a lot on Skylake, where AVX512
is disabled by default. When it is enabled, we can suddenly reproduce the same crashes on
Skylake too.

I have pushed a fix for this issue.


On 31 Oct 2022, at 04:35, Liang Mao < at< at>> wrote:

Hi Stefan and ZGC team,

I see crashes as well with early access build. The command line is
"java -XX:+UseZGC -Xmx8g -Xms8g -Xlog:gc* -XX:ParallelGCThreads=8 -XX:ConcGCThreads=2 -jar specjbb2015.jar -m COMPOSITE".
It works well in Intel sky-lake machines but consistently crashes in an Ice-lake architecture
"Intel(R) Xeon(R) Platinum 8369B CPU @ 2.90GHz" machine in 3 minutes. Hope this can help.


From:Stefan Karlsson <stefan.karlsson at<mailto:stefan.karlsson at>>
Send Time:2022 Oct. 19 (Wed.) 19:44
To:"Kemper, William" <kemperw at<mailto:kemperw at>>; zgc-dev at<mailto:zgc-dev at> <zgc-dev at<mailto:zgc-dev at>>
Subject:Re: Generational ZGC crashes on specbjbb

Thanks a lot!

I'll see if I can figure out a way to reproduce this in-house.


On 2022-10-18 23:39, Kemper, William wrote:
Filed: - Please let me know if you need anymore data. We're excited about Generational ZGC!

From: Stefan Karlsson <stefan.karlsson at><mailto:stefan.karlsson at>
Sent: Tuesday, October 18, 2022 11:57:47 AM
To: Kemper, William; zgc-dev at<mailto:zgc-dev at>
Subject: RE: [EXTERNAL]Generational ZGC crashes on specbjbb

CAUTION: This email originated from outside of the organization. Do not click links or open attachments unless you can confirm the sender and know the content is safe.

Thanks for reporting. If you file a JBS entry I'll figure out the best way to tag issues around Generational ZGC.


On 2022-10-18 20:20, Kemper, William wrote:
How do you want to handle error reports? I didn't see how to open an issue on GitHub. Should I open a ticket on JBS? Is there a label to distinguish ZGC generational from non-generational?

Thank you,

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