RFR: 8278020: ~13% variation in Renaissance-Scrabble [v2]

[Vladimir Kozlov]

On Wed, 15 Dec 2021 06:02:35 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> I approved but still think this should be targeted at 18 - assuming this was a performance regression in 18.
>> 
>> Padding may have the same performance affect but will also impact footprint potentially - which in turn may impact the caching behaviour.
>
>> I approved but still think this should be targeted at 18 - assuming this was a performance regression in 18.
>> 
>> Padding may have the same performance affect but will also impact footprint potentially - which in turn may impact the caching behaviour.
> 
> I suggested padding only as experiment to prove Ioi's theory.  Current changes are good as the fix.

>> @vnkozlov I found that most Klasses in CDS are preceded by a Method. Does the jitted code write into a Method often?
> Method counters? May be worth spreading them out better, or to pad them to prevent false sharing.

I don't think compiled code updates something in Method. We need to look on fields layout.
Compiled code do update frequently MethodCounters (invocations, loops) and  MethodData (profiling counters for bytecode). Both are allocated in metaspace as classes.

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PR: https://git.openjdk.java.net/jdk/pull/6838