RFR 8221507: Implement JFR Events for Shenandoah

[Roman Kennke]

> On Tue, Mar 26, 2019 at 5:16 PM Roman Kennke <rkennke at redhat.com 
> <mailto: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.

Hmm, ok. This only ever happens when regions change state, right? I 
doubt that this is frequent enough to make an actual difference. I 
suspect that what you see is noise. I'm good. Let's also hear Aleksey's 
opinion though.

Thanks!
Roman


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