RFR 8221507: Implement JFR Events for Shenandoah

[Zhengyu Gu]

On 3/29/19 4:28 PM, Ken Dobson wrote:
> On Tue, Mar 26, 2019 at 5:16 PM Roman Kennke <rkennke at redhat.com> wrote:
> 
>>> Please review this patch that adds support for two new JFR events
>>> ShenandoahHeapRegionStateChange and ShenandoahHeapRegionInformation.
>>>
>>> Bug: https://bugs.openjdk.java.net/browse/JDK-8221507
>>> Webrev: http://cr.openjdk.java.net/~kdobson/53476/webrev/
>>>
>>> The events appears to result in ~2% overhead though there is some
>>> uncertainty as to whether some of that is noise.
>>>
>>> Thanks,
>>>
>>> Ken Dobson
>>
>> Very nice!
>>
>> The overhead is only present with JFR active, I assume?
>>
>> We've noticed that there is some overhead when JFR is included in the jdk
> but not running. This may be because the event object has to be
> instantiated at each transition whether it's enabled or not. You can see
> the exact numbers in the email I previously sent you.
If it is the case (although, I am skeptic about it), we should file 
upstream JFR RFE to provide static method for should_commit().

-Zhengyu



> 
> Have you run hotspot_gc_shenandoah tests?
>>
>> Yes and all of the tests pass.
> 
> Thanks,
> 
> Ken Dobson
>