[14] RFR 8230765: Implement nmethod barrier for x86_32 platforms

[Erik Österlund]

Hi Zhengyu,

Looks good; ship it.

Thanks
/Erik

> On 26 Nov 2019, at 19:07, Zhengyu Gu <zgu at redhat.com> wrote:
> 
> Hi Erik,
> 
> On 11/26/19 8:24 AM, Zhengyu Gu wrote:
>>> Here is a patch with my proposed cleanup:
>>> http://cr.openjdk.java.net/~eosterlund/8230765/webrev.02/
>>> 
>>> Incremental:
>>> http://cr.openjdk.java.net/~eosterlund/8230765/webrev.01_02/
>>> 
>> Yes, this indeed a much cleaner approach. I will take your proposed cleanup and run through submit.
> 
> I took your patch. There is just one little hiccup: compiler expects intptr_t instead of int* on x86_32, the fix is straightforward.
> 
>   __ push(tmp);
> -  __ movptr(tmp, bs_nm->disarmed_value_address());
> +  __ movptr(tmp, (intptr_t)bs_nm->disarmed_value_address());
>   Address disarmed_addr(tmp, 0);
>   __ align(4);
>   __ cmpl(disarmed_addr, 0);
> 
> 
> Full webrev: http://cr.openjdk.java.net/~zgu/JDK-8230765/webrev.02/
> 
> and patch passed submit tests.
> 
> Okay to push?
> 
> Thanks,
> 
> -Zhengyu
> 
> 
>> -Zhengyu
>>> Thanks,
>>> /Erik
>>> 
>>>> On 11/25/19 9:35 PM, Zhengyu Gu wrote:
>>>>> Hi all,
>>>>> 
>>>>> Please review this implementation of nmethod barrier for x86_32 platforms.
>>>>> 
>>>>> x86_32 implementation mirrors x86_64's. The only difference is where it reads nmethod disarmed value.
>>>>> 
>>>>> Unlike 64-bits, 32-bits platform does not have a dedicated register for current thread. So that it is cheaper to read disarmed value from global location than from per-thread GC data.
>>>>> 
>>>>> Currently, only Shenandoah GC uses the implementation for its concurrent class unloading. This implementation, along with Shenandoah concurrent class unloading, has been baked in shenandoah/jdk repo for some time now,  they are ready for integration.
>>>>> 
>>>>> 
>>>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8230765
>>>>> Webrev: http://cr.openjdk.java.net/~zgu/JDK-8230765/webrev.01/
>>>>> 
>>>>> 
>>>>> Test:
>>>>>   hotspot_gc with x86_64 and x86_32 JVM on Linux
>>>>>   Submit test.
>>>>> 
>>>>> Thanks,
>>>>> 
>>>>> -Zhengyu
>>>>> 
>>> 
>