RFR: 8240370: Provide Intel JCC Erratum opt-out

[Vladimir Ivanov]

Looks good.

Best regards,
Vladimir Ivanov

> On 3 Mar 2020, at 19:35, Erik Österlund <erik.osterlund at oracle.com> wrote:
> 
> 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
>>> 
>