RFR: 8240370: Provide Intel JCC Erratum opt-out

[Erik Österlund]

Hi Vladimir,

Thanks for the review.

/Erik

> On 3 Mar 2020, at 18:06, Vladimir Ivanov <vladimir.x.ivanov at oracle.com> wrote:
> 
> 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
>>>> 
>> 
>