RFR: 8160539: Stack frame scanning acquires DerivedPointerTableGC_lock mutex

[Vladimir Kozlov]

LGTM.

Thanks,
Vladimir

On 5/10/19 5:13 PM, Kim Barrett wrote:
> Please review this change in the representation of the derived pointer table.
> It was a GrowableArray of pointers to derived pointer entries, protected by
> the DerivedPoitnerTableGC_lock.  It is changed to a LockFreeStack of such
> entries.
> 
> Running specjbb2015 with an instrumented VM found occasional contention for
> that lock; roughly half of the attempts to lock it found it already held by
> another thread.  Comparing averages for G1 Thread Roots times for specjbb2015
> before and after the change, average was reduced by 8% (1ms), max by 16%
> (11.5ms), and total by 8% (27ms).  Since the code involved is largely
> GC-agnostic, other collectors (except Serial) should see similar improvements.
> 
> DerivedPointerTable::update_pointers() showed no significant change; it only
> takes about 0.1ms with or without the change of representation.
> 
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8160539
> 
> Webrev:
> http://cr.openjdk.java.net/~kbarrett/8160539/open.00/
> 
> Testing:
> mach5 tier1-5, plus the above mentioned specjbb2015 performance testing.
> 
>