RFR: 8221554: aarch64 cross-modifying code [v3]

[Andrew Haley]

On 11/12/20 5:28 PM, Alan Hayward wrote:
> On Fri, 23 Oct 2020 10:17:09 GMT, Andrew Haley <aph at openjdk.org> wrote:
> 
>>> src/hotspot/cpu/aarch64/macroAssembler_aarch64.cpp line 5317:
>>>
>>>> 5315: #endif
>>>> 5316: }
>>>> 5317: 
>>>
>>> Unless VerifyCrossModifyFence is turned on in debug builds it will almost never be used. Please turn this on by default in AArch64 debug builds.
>>
>> Please...
> 
> Aha - Looks like your comments hadn't been made public until now.

"Hadn't been made public?" There's a way to comment without the owner
of the PR being able to see the comments?

> The problem is it massively slows down a run. A tier1 test run for fastdebug went from 1h 32m 58s to 
> 3h 43m 47s. I didn't think that would be acceptable.

But why is it so expensive? All it does is mark the threads at a safepoint
and later check the mark at safepoints. It's not as if it's doing anything
much, but you're telling me it is more expensive than everything else put
together.

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