RFR: 8277137: Set OnSpinWaitInst/OnSpinWaitInstCount defaults to "isb"/1 for Arm Neoverse N1 [v3]

[Andrew Haley]

On Wed, 17 Nov 2021 12:31:10 GMT, Evgeny Astigeevich <duke at openjdk.java.net> wrote:

>> One `ISB` implementation of `Thread.OnSpinWait` shows performance improvements on Graviton2 (Arm Neoverse N1 implementation), e.g. https://github.com/openjdk/jdk/pull/5562#issuecomment-966153163. 
>> 
>> Testing:
>> - `make test TEST=gtest`: Passed
>> - `make run-test TEST=tier1`: Passed
>> - `make run-test TEST=tier2`: Passed
>> - `make run-test TEST=hotspot/jtreg/compiler/onSpinWait`: Passed
>
> Evgeny Astigeevich has updated the pull request incrementally with one additional commit since the last revision:
> 
>   Set defaults for OnSpinWaitInst/OnSpinWaitInstCount independently

Marked as reviewed by aph (Reviewer).

Hi,

> > Did we establish that this is the right default for Neoverse N1?
> 
> This is based on:
> 
>     * MySql: https://bugs.mysql.com/bug.php?id=100664
> 
>     * MongoDB: https://jira.mongodb.org/browse/WT-6872
> 
>     * Netty: [Use cpu_relax() implementation for aarch64 netty/netty#11677](https://github.com/netty/netty/pull/11677)
> 
>     * Customers' benchmarks and workloads.
> 
>     * Experiments with two and three `ISB` instructions.

OK, I'll buy that.

-------------

PR: https://git.openjdk.java.net/jdk/pull/6415