RFR(S): 8229422: Taskqueue: Outdated selection of weak memory model platforms
aph at redhat.com
Tue Jan 14 15:08:42 UTC 2020
On 1/14/20 3:05 PM, Andrew Haley wrote:
> On 1/14/20 3:00 PM, Andrew Haley wrote:
>> On 8/15/19 4:49 PM, Derek White wrote:
>>> However, setting CPU_MULTI_COPY_ATOMIC for AArch64 would result in changing behavior (removing fence in taskqueue) that should be looked at and tested by the aarch64 folks, so if Andrew Haley agrees, I suggest deferring changing this AArch64 behavior to a separate issue.
>> Well, yes. What i don't understand is what any of this has to do with
>> multi-copy atomicity. The fence is needed for _age.get() on all machines
>> with relaxed memory consitency, AFAICS.
> Ah, I found the answer in another thread:
"No, the problem is not reordering. The problem is that _bottom,
which is read after _age, might be older than _age because another
processor didn't write it back yet. The fence (sync) makes the
current thread wait until it has the new _bottom.
"On Power, a write is not visible to all other threads simultaneously
So, my question: on a machine with relaxed memory, do we still need an acquire
Andrew Haley (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
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