[crac] RFR: 8368929: [CRaC] Move CPUFeatures check to C/R engine [v10]

[Radim Vansa]

On Wed, 8 Oct 2025 08:36:43 GMT, Timofei Pushkin <tpushkin at openjdk.org> wrote:

>> Radim Vansa has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Fix include problems
>
> src/hotspot/share/runtime/crac.cpp line 107:
> 
>> 105: 
>> 106:   // If this is a second checkpoint we should use a clear configuration
>> 107:   if (_generation != 0 && !_engine->reset_conf()) {
> 
> Why do we need to reset the configuration now? Is it because user data is auto-reset while the tags are not? Ideally they should act the same to make the behavior more predictable. IMO it would be better if both were kept until explicitly cleared by the user, if that is possible. But that would require updating the user data API probably...
> 
> Anyway, shouldn't the CPU features stay the same between checkpoints? Then it would be more efficient to set them only on the first checkpoint instead of resetting the whole configuration each time.

Hmm, the reset was there to prevent errors coming from setting the CPU features second time, but you're right that rather than that we could just avoid setting them in the second checkpoint.

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PR Review Comment: https://git.openjdk.org/crac/pull/266#discussion_r2416989366