RFR: 8240370: Provide Intel JCC Erratum opt-out

[Tobias Hartmann]

Hi Erik,

looks good to me too.

Best regards,
Tobias

On 03.03.20 18:27, Erik Österlund wrote:
> 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
>>>>>
>>>
>>
>