[9] RFR (M): 8086053: Address inconsistencies regarding ZeroTLAB

[Zoltán Majó]

Hi Vladimir,


On 01/11/2016 08:26 PM, Vladimir Kozlov wrote:
> Don't use GC flags in the test. They will conflict with flags passed 
> by testing infra and the test will fail. The was bug fixed by removing 
> GC flags from all our tests.
> Note, Nightly testing does GC flags rotation so you don't need to do 
> that.

OK, I removed all GC flags from the test. Here is the updated webrev:
http://cr.openjdk.java.net/~zmajo/8086053/webrev.03/

> Otherwise looks good.

Thank you for the review! I'll push webrev.03 today as it addresses all 
issues that were brought up.

Thank you and best regards,


Zoltan

>
> Thanks,
> Vladimir
>
> On 1/11/16 5:37 AM, Zoltán Majó wrote:
>> Hi,
>>
>>
>>
>> On 01/11/2016 02:11 PM, Zoltán Majó wrote:
>>> [...]
>>> Yes, that is a good idea. I added a test that launches the VM with 
>>> all flag combinations and also with different GCs.
>>> I did the same what the test does to reproduce the original failure.
>>>
>>> Here is the updated webrev:
>>> http://cr.openjdk.java.net/~zmajo/8086053/webrev.01/
>>
>> The test contains and unnecessary @library tag and package import. 
>> The year in the copyright statement must be changed
>> as well (to 2016).
>>
>> Here is the webrev with those changes:
>> http://cr.openjdk.java.net/~zmajo/8086053/webrev.02/
>>
>> Sorry for the noise.
>>
>> Thank you and best regards,
>>
>>
>> Zoltan
>>
>>
>>>
>>> The newly added test passes on all supported platforms.
>>>
>>> Thank you and best regards,
>>>
>>>
>>> Zoltan
>>>
>>>>
>>>> Best,
>>>> Tobias
>>>>
>>>>
>>>> On 08.01.2016 12:06, Zoltán Majó wrote:
>>>>> Hi,
>>>>>
>>>>>
>>>>> please review the patch for 8086053.
>>>>>
>>>>> https://bugs.openjdk.java.net/browse/JDK-8086053
>>>>>
>>>>> Problem: With ZeroTLAB enabled, the GC is supposed to zero-fill 
>>>>> newly allocated TLAB regions. With ZeroTLAB
>>>>> disabled, the interpreter and compiled code should assume the 
>>>>> responsibility to zero-fill newly allocated regions.
>>>>> Currently, the handling of the ZeroTLAB flag shows some 
>>>>> inconsistencies between the GC and the compilers. These
>>>>> inconsistencies lead to newly allocated regions not being filled 
>>>>> with zeros.
>>>>>
>>>>> Solution: Address the following:
>>>>> - With -XX:+FastTLABRefill, C1-compiled code refills the TLAB 
>>>>> without notifying the GC. As a result, the newly
>>>>> allocated TLAB is not initialized with zero. Add TLAB 
>>>>> initialization code to C1.
>>>>> - With -XX:+ZeroTLAB, the C2 compiler skips zero-initialization of 
>>>>> newly allocated objects/arrays even if TLAB
>>>>> allocation is disabled. Add stricter conditions to C2 on when to 
>>>>> skip filling objects/arrays with zero.
>>>>>
>>>>> Webrev:
>>>>> http://cr.openjdk.java.net/~zmajo/8086053/webrev.00/
>>>>>
>>>>> Testing:
>>>>> - local testing (linux_x86_64) of failing test case with 
>>>>> -XX:+UseG1GC and -XX:+UseSerialGC;
>>>>> - JPRT;
>>>>> - all hotspot tests on all platforms affected by the change using 
>>>>> all combinations of +/-UseTLAB and +/-ZeroTLAB.
>>>>>
>>>>> Thank you and best regards,
>>>>>
>>>>>
>>>>> Zoltan
>>>>>
>>>
>>