[jdk16] RFR: 8259765: ZGC: Handle incorrect processor id reported by the operating system [v2]

[Per Liden]

On Sat, 16 Jan 2021 13:00:04 GMT, David Holmes <dholmes at openjdk.org> wrote:

>> Per Liden has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Review
>
> So we have to penalize all correctly functioning users because of one broken environment? Can we not detect this broken environment at startup and inject a workaround then?
> 
> Why is this an environment that is important enough that OpenJDK has to make changes to deal with a broken environment?
> 
> Cheers,
> David

@dholmes-ora 

> So we have to penalize all correctly functioning users because of one broken environment? Can we not detect this broken environment at startup and inject a workaround then?

Not sure what you have in mind here? Having an indirect function call would not result in a lower overhead than the test/branch I've introduced. It's also not necessarily trivial to detect this error at startup, as you would need a reliable way to enumerate all processors (something that seems semi-broken in this environment, which is the root of the problem), bind the current thread to each of them and then check the processor id.

> Why is this an environment that is important enough that OpenJDK has to make changes to deal with a broken environment?

That's of course always judgement call/trade-off. I can't say I have a super good understanding of how common this environment it, but there's at least one "Java cloud provider" that uses this environment.

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PR: https://git.openjdk.java.net/jdk16/pull/124