AOT code usage restrictions

[Ashutosh Mehra]

>
> 3. In a future, when user requested during training run (with VM's
> flag[s]), we will allow to use AOT code generated for old CPU
> instructions (for example, AVX2) on machines with new instructions (for
> example, AVX512) by restricting online (normal JIT) code generation to
> old CPU instructions. This will allow to use the same cached AOT code on
> variety of machines. But you may not get the best peak performance on
> newer machines.


Shouldn't this be a production run flag, rather than a training run flag?

Thanks,
- Ashutosh Mehra


On Thu, Jan 22, 2026 at 10:14 PM Charles Oliver Nutter <headius at headius.com>
wrote:

> Commenting from a user perspective, since we very much want to ship AOT
> caches for JRuby users...
>
> The restriction seems fine largely because I don't know how else you'd
> work around it. But I think with this restriction there needs to be a clear
> way to AOT for a lowest common denominator without having that exact
> hardware on hand. I don't want to have to find some janky old x86 machine
> to train a portable cache on.
>
> On Thu, Jan 22, 2026, 20:05 Vladimir Kozlov <vladimir.kozlov at oracle.com>
> wrote:
>
>> Hi,
>>
>> I would like to get opinion from community regarding AOT code usage
>> restrictions for JEP https://openjdk.org/jeps/8335368.
>>
>> For current AOT features in JDK 25 and 26 it is not the issue - CPU
>> features do not affect them.
>>
>> CPU features affect generated AOT code - the instructions set is defined
>> by machine on which AOT training is done. But CPU instructions on
>> machine where AOT cache is used could be different.
>>
>> Our current proposal is next:
>>
>> 1. The best startup and peak performance with AOT code could be achieved
>> when training and production runs use the same type of machines (same
>> CPU and OS).
>>
>> 2. AOT code will not be used if CPU features on machine for production
>> run does not match one used for training. Other AOT features (cached
>> classes and profiling info) will still be used.
>>
>> 3. In a future, when user requested during training run (with VM's
>> flag[s]), we will allow to use AOT code generated for old CPU
>> instructions (for example, AVX2) on machines with new instructions (for
>> example, AVX512) by restricting online (normal JIT) code generation to
>> old CPU instructions. This will allow to use the same cached AOT code on
>> variety of machines. But you may not get the best peak performance on
>> newer machines.
>>
>> What do you think about this proposal?
>>
>> Thanks,
>> Vladimir K
>>
>>
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