RFR: 8345289: RISC-V: enable some extensions with hwprobe

[Fei Yang]

On Tue, 3 Dec 2024 09:34:25 GMT, Hamlin Li <mli at openjdk.org> wrote:

>> Hi,
>> Can you help to review the patch?
>> Currently, some extensions are not enable automatically with hwprobe, this is to enable them with hwprobe result.
>> 
>> Thanks!
>> 
>> Tests running so far so good.
>
> I think you're right, I'll only check and enable zicboz in this pr.

Hi @Hamlin-Li

> I think you're right, I'll only check and enable zicboz in this pr.

Please update the PR title to reflect the latest change. And I have two comments here.
1. It would be nice if we have some JMH or benchmark tests to show the performance benefit.
2. Regarding the cache line size, we assume `CacheLineSize` is 64 bytes for now. But that doesn't seem safe.
    Starting from linux-6.7, we have `RISCV_HWPROBE_KEY_ZICBOZ_BLOCK_SIZE` hwprobe to get the real size at JVM startup.
    For safety consideration, I prefer to get this cache-line size auto-detection resolved before this one.

Let me know what you think. Thanks.

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

PR Comment: https://git.openjdk.org/jdk/pull/22474#issuecomment-2566078154