RFR: AArch64: 8179954: AArch64: C1 and C2 volatile accesses are not sequentially consistent (original) (raw)

Stuart Monteith stuart.monteith at linaro.org
Thu May 11 15:34:13 UTC 2017

Hi, It looks fine as far as I can tell. Could the comment be explicit about replacing the code sequence:

STLR LDR DMB

with: STLR DMB LDR

as initially, I was thinking about them being on different threads. (although, looking at the thread, it was probably just me that thought that).

BR, Stuart

On 11 May 2017 at 13:31, Andrew Haley <aph at redhat.com> wrote:

Thanks for finding that bug. It's a reminder that we need to concentrate on doing the minimum at this stage to ensure correctness. Our performance is good, and this change is not hugely profitable. It's not worth risking the whole ship for.

Nevertheless, I've made a new webrev, which does the right thing. I stepped through the code to make sure. I've come this far, so I might as well get it right. (Yes, I'm aware that I just fell into the sunk cost fallacy, but I want something to show for the work I've done.) http://cr.openjdk.java.net/~aph/8179954-3/ In JDK 10 we should look at replacing all the explicit fences used for volatiles with LDAR/STLR. OK? I'd like two reviewers for this one. Andrew.

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