RFR: 8323641: Test compiler/loopopts/superword/TestAlignVectorFuzzer.java timed out [v2]

[Christian Hagedorn]

On Mon, 15 Jan 2024 07:43:45 GMT, Emanuel Peter <epeter at openjdk.org> wrote:

>> It seems that allowing `90%` of the timeout-time was cutting it too close. Some individual tests can take more time occasionally, one even took more than `80 sec` (very rare).
>> 
>> Why do these tests take so long?
>> - Sometimes compilation can take quite a bit of time. `-XX:LoopUnrollLimit=250` already increases the number of nodes allowed in a loop-body, and with unrolling this increases significantly. SuperWord then has to work through all these nodes, and has a lot of quadratic and higher complexity loops.
>> - The loop bodies are quite large (hand unrolled), and often lead to partial vectorization, with lots of scalar memory ops. This produces quite sub-optimal code, with a bit too many instructions in the loop body. Combined with lots of array copying, this probably takes quite a hit on caches.
>> 
>> I will investigate SuperWord compilation time in the future, and lower the runtime complexity if neccessary/possible, it is part of my autovectorization plans.
>> 
>> I now lowered the allowance down to `40%`, which is hopefully small enough to avoid timeout, while still allowing sufficient many run to get decent test coverage.
>
> Emanuel Peter has updated the pull request incrementally with one additional commit since the last revision:
> 
>   camelCase for local variable, for Christian

Marked as reviewed by chagedorn (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/17389#pullrequestreview-1821118498