[crac] RFR: RFC: -XX:CPUFeatures=0xnumber for CPU migration [v24]

[Jan Kratochvil]

On Wed, 31 May 2023 09:07:48 GMT, Anton Kozlov <akozlov at openjdk.org> wrote:

>> Jan Kratochvil has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   +-XX:CPUFeatures=ignore
>
> src/hotspot/cpu/x86/vm_version_x86.cpp line 648:
> 
>> 646:   if (strcmp(ccstr, "ignore") == 0) {
>> 647:     return _features;
>> 648:   }
> 
> Should not be here `ignore_glibc_not_using = true` ? I cannot see a place where ignore_glibc_not_using is set to true, could you point?

I agree, fixed.

> src/hotspot/cpu/x86/vm_version_x86.cpp line 1319:
> 
>> 1317:     if (ShowCPUFeatures) {
>> 1318:       if (ignore_glibc_not_using) {
>> 1319: 	tty->print_cr("CPU features are being kept intact as requested by -XX:CPUFeatures=ignore");
> 
> Could you check whitespace error https://github.com/openjdk/crac/pull/41/checks?check_run_id=13867663789

Sorry, I have provided some local reconfigurations so that it hopefully should not happen again.

> src/hotspot/cpu/x86/vm_version_x86.cpp line 1335:
> 
>> 1333:     glibc_not_using(      features_expected & ~      _features,
>> 1334: 		    glibc_features_expected & ~_glibc_features);
>> 1335:   }
> 
> I'm trying the code, and getting
> 
> 
> anton at mercury:~/proj/crac$ ./build/linux-x86_64-server-release/images/jdk/bin/java -XX:+ShowCPUFeatures -XX:CPUFeatures=generic -version
> This machine's CPU features are: -XX:CPUFeatures=0x61805fdfbff,0x1e6
> CPU features being used are: -XX:CPUFeatures=0x200000080d7,0x0
> openjdk version "17-internal" 2021-09-14
> OpenJDK Runtime Environment (build 17-internal+0-adhoc..crac)
> OpenJDK 64-Bit Server VM (build 17-internal+0-adhoc..crac, mixed mode, sharing)
> 
> 
> I would expect re-exec, but for some reason it was not perfromed?

That was a regression/bug, thanks, fixed.

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

PR Review Comment: https://git.openjdk.org/crac/pull/41#discussion_r1211725314
PR Review Comment: https://git.openjdk.org/crac/pull/41#discussion_r1211722499
PR Review Comment: https://git.openjdk.org/crac/pull/41#discussion_r1211726817