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

[Liu Xin]

Hi, Andrew and Felix,

I did backport as Felix suggested. To get UseCondCardMark, we need to
backport other 3 patches.

hg qseries as follows ( applied in order)
8076987: https://cr.openjdk.java.net/~xliu/8076987/00/webrev/
8078438: https://cr.openjdk.java.net/~xliu/8078438/00/webrev/
8079315: https://cr.openjdk.java.net/~xliu/8079315/00/webrev/
8135018: https://cr.openjdk.java.net/~xliu/8135018/02/webrev/

As Andrew pointed out, I also notice that it introduces a storeLoad membar
for interpreter if UseCondCardMark is on.
The reason I didn't backport UseCondCardMark at first place because it's
off by default. I need to run all tests again with the new parameter
-XX:+UseCondCardMark to validate it.  Another reason is that all
performance evaluation was done on x86_64.
It's really time consuming to evaluate performance impact on aarch64.  So I
shortcut to fix my primary bug.

Could you sponsor my previous webrev?
https://cr.openjdk.java.net/~xliu/8135018/01/webrev/

It does have a conflict with c1_LIRGenerator.cpp. How about I send another
webrev to jdk8u and update it as well?

thanks,
--lx


On Mon, Dec 16, 2019 at 1:00 AM Andrew Haley <aph at redhat.com> wrote:

> 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
> EAC8 43EB D3EF DB98 CC77 2FAD A5CD 6035 332F A671
>
>