RFR: 8316180: Thread-local backoff for secondary_super_cache updates [v5]

[Aleksey Shipilev]

On Wed, 27 Sep 2023 15:34:13 GMT, Vladimir Ivanov <vlivanov at openjdk.org> wrote:

>> Aleksey Shipilev has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Denser AArch64
>
> src/hotspot/share/runtime/globals.hpp line 2003:
> 
>> 2001:           range(0, UINT_MAX)                                                \
>> 2002:                                                                             \
>> 2003:   product(uint, SecondarySuperMissBackoff, 1000, EXPERIMENTAL,              \
> 
> Should it be marked DIAGNOSTIC instead? The functionality is turned on by default. It it were 0 by default, EXPERIMENTAL would have been well-justified.

I don't think the discriminating factor for calling an option "diagnostic" or "experimental" is its default value. Rather it is its target use.

As per `globals.hpp`:


// DIAGNOSTIC options are not meant for VM tuning or for product modes.
//    They are to be used for VM quality assurance or field diagnosis
//    of VM bugs.

// EXPERIMENTAL flags are in support of features that may not be
//    an officially supported part of a product, but may be available
//    for experimenting with. They could, for example, be performance
//    features that may not have undergone full or rigorous QA, but which may
//    help performance in some cases and released for experimentation
//    by the community of users and developers. 


...and this one is obviously the experimental performance feature.

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PR Review Comment: https://git.openjdk.org/jdk/pull/15718#discussion_r1338871123