RFR: 8310949: RISC-V: Initialize UseUnalignedAccesses [v5]

[Robbin Ehn]

On Wed, 28 Jun 2023 09:30:31 GMT, Vladimir Kempik <vkempik at openjdk.org> wrote:

> One case to consider: lets say I have a system with X big cores ( which support MISALIGNED_FAST) and X small cores ( with MISALIGNED_EMU)
> 
> if I run some java workload on all cores, what should hw_prober return ? obvious result here is to use +AvoidUnallignedAccesses.
> 
> If I run same java workload but use taskset to run it only on big cores, how will jdk's hw_prober code work ? should it work properly and disable AvoidUnallignedAccesses or it's too much and one need to manually set -XX:-AvoidUnallignedAccesses ?

FYI:
The only way today using hwprobe in example above is to query each cpu individually to find the cpu set that have fast and the cpu set have emulated. (or vector or any other extension which may differ)
I have proposed that hwprobe should be able to also return a cpu set for some set of features.
To either inform user of what affinity they should use, or if we want change the affinity of the VM automagically.

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PR Comment: https://git.openjdk.org/jdk/pull/14676#issuecomment-1611111768