[aarch64-port-dev ] RFR 8135018: AARCH64: Missing memory barriers for CMS collector

[Andrew Haley]

On 12/14/19 4:47 AM, Liu Xin wrote:
> I trace the feature UseCondCardMark. It was
> introduced by the following changes.
> https://bugs.openjdk.java.net/browse/JDK-8076987 C1
> https://bugs.openjdk.java.net/browse/JDK-8078438 interpreter
> UseCondCardMark is only supported by C2 currently.

UseCondCardMark was supposed to be a performance enhancement for
very large multi-core systems, but we realized that it needed a
StoreLoad barrier. Because StoreLoad is so expensive there is no
performance advantage, therefore as far as I can see the whole
UseCondCardMark exercise is a waste of time. There is no point
back-porting changes to the interpreter and C1.

Unless someone does some performance measurements to prove that
there is some performance gain in C1 and the interpreter,
UseCondCardMark changes should not be back-ported.

-- 
Andrew Haley  (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
https://keybase.io/andrewhaley
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