RFR: 8240370: Provide Intel JCC Erratum opt-out

[Erik Österlund]

Hi Tobias,

Thanks for the review.

/Erik

> On 5 Mar 2020, at 08:09, Tobias Hartmann <tobias.hartmann at oracle.com> wrote:
> 
> 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
>>>>>> 
>>>> 
>>> 
>>