[aarch64-port-dev ] Question about JVM option "-XX:+UseBarriersForVolatile" usage in aarch64.

[Nick Gasson]

On 04/02/20 21:22 pm, Andrew Dinn wrote:
> One reason for having this switch was to provide a comparator for our
> scheme to implement the Java volatile accesses using ldar/stlr. That
> translation scheme avoids a dmb after the stlr allowing the value being
> written to be committed lazily while still providing the critical
> guarantee that prior writes are committed before it gets committed. The
> switch ensures we can fall back to a 'reference' implementation based on
> dmbs that, amongst other things, enforces immediate commit of the
> volatile write after commit of its predecessors.
>
> By removing support we lose the ability to test cases where
> synchronization errors occur with our scheme by switching to the
> 'standard' model. That may still be useful for finding bugs (current or
> newly injected) in our translation and, indeed, in new HW.

OK, but keeping it is not without cost. If UseBarriersForVolatile is to
have value as a reference implementation we need to expend effort to
test it and fix any bugs that arise from changes to other parts of the
code (see Xiaohong's original mail).


Thanks,
Nick