[crac] RFR: RFC: -XX:CPUFeatures=0xnumber for CPU migration [v2]

[Jan Kratochvil]

On Fri, 10 Feb 2023 14:12:22 GMT, Ashutosh Mehra <duke at openjdk.org> wrote:

> To enable/disable extended instruction sets, hotspot already has options (like UseSSE). Combining those options with `CPUFeatures=[generic|native]` or `PortableCode` would provide an easier way for the user to control the cpu features that hotspot should use.

I did not expect anyone would study which CPU model should use which `UseSSE`, `UseAVX`, `UseCLMUL` and other options.

The current code just prints `You have to specify -XX:CPUFeatures=0x421801fcfbd7 during -XX:CRaCCheckpointTo` as described in the Comment 0. So one should just run it once on the oldest farm machine and copy/paste the number to the snapshotting script. Or just to run it on all of the farm machines and do a logical AND of all the numbers if one is unsure which machine is the oldest one in your farm.

I sure do not mind which options should be used. I agree `-XX:CPUFeatures=[generic|native]` would be useful (`native` not so useful as it is the current OpenJDK default).

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

PR: https://git.openjdk.org/crac/pull/41