RFR: 8240370: Provide Intel JCC Erratum opt-out

[Erik Österlund]

Hi Vladimir,

Sure, why not. I liked the second alternative:
http://cr.openjdk.java.net/~eosterlund/8240370/webrev.02/

Thanks,
/Erik

On 2020-03-03 16:29, Vladimir Ivanov wrote:
> Hi Erik,
>
>> New webrev: http://cr.openjdk.java.net/~eosterlund/8240370/webrev.01/
>
> IMO it makes sense to support both forcibly turning the flag on and 
> off from the command-line.
>
> So, I prefer:
>
>   bool VM_Version::compute_has_intel_jcc_erratum() {
> +  if (!FLAG_IS_DEFAULT(IntelJccErratumMitigation)) {
> +    return IntelJccErratumMitigation;
> +  }
>
> Or even:
>
>   if (FLAG_IS_DEFAULT(IntelJccErratumMitigation)) {
>     _has_intel_jcc_erratum = compute_has_intel_jcc_erratum();
>   } else {
>     _has_intel_jcc_erratum = IntelJccErratumMitigation;
>   }
>
> Best regards,
> Vladimir Ivanov
>
>>> /Claes
>>>
>>> On 2020-03-03 13:23, Erik Österlund wrote:
>>>> Hi,
>>>>
>>>> Today, the Intel JCC Erratum mitigation is automatically enabled 
>>>> when running on an affected machine.
>>>> While it is strongly recommended that customers run code in 
>>>> environments with the micro code updates
>>>> provided by Intel to mitigate the erratum, and hence are probably 
>>>> almost always better off with the
>>>> mitigation, there could be value in being able to opt out to 
>>>> analyze the performance characteristics
>>>> of an application, as a diagnostic option.
>>>>
>>>> This patch adds a diagnostic option that allows you to opt out 
>>>> with: -XX:-IntelJccErratum
>>>>
>>>> Webrev:
>>>> http://cr.openjdk.java.net/~eosterlund/8240370/webrev.00/
>>>>
>>>> Bug:
>>>> https://bugs.openjdk.java.net/browse/JDK-8240370
>>>>
>>>> Thanks,
>>>> /Erik
>>