RFR: 8203319: JDK-8201487 disabled too much queue balancing

[Stefan Johansson]

On 2018-06-04 20:31, Kim Barrett wrote:
>> On May 31, 2018, at 3:34 PM, Kim Barrett <kim.barrett at oracle.com> wrote:
>>
>>> On May 31, 2018, at 4:41 AM, Stefan Johansson <stefan.johansson at oracle.com> wrote:
>>>
>>>
>>>
>>> On 2018-05-30 19:33, Kim Barrett wrote:
>>>> Please review this change to the ReferenceProcessor's test for whether
>>>> to balance a set of queues before processing them with multiple
>>>> threads.  The change to that test made by JDK-8201487 doesn't peform
>>>> balancing for some (potential, see Testing below) states where not
>>>> doing so will result in some discovered References not being
>>>> processed.  In particular, there are cases where we must ignore
>>>> -XX:-ParallelRefProcBalancingEnabled and balance anyway.
>>>> We also now avoid balancing in some cases where we know the set is
>>>> already balanced, even with -XX:+ParallelRefProcBalancingEnabled.
>>>> CR:
>>>> https://bugs.openjdk.java.net/browse/JDK-8203319
>>>> Webrev:
>>>> http://cr.openjdk.java.net/~kbarrett/8203319/open.00/
>>> Looks good,
>>> Stefan
>>
>> Thanks, Stefan.
> 
> The new need_balance_queues function has an optimization to avoid
> balancing in a case where we already know the queues are balanced.
> This assumes it's being called for initial balancing after discovery,
> and not for some re-balancing after a processing phase.  But that's
> problematic for JDK-8043575 (recently RFR'ed).  And if we're already
> balanced, balance_queues doesn't have very much to do.  (And
> eventually the optimization would be rendered moot anyway, by the
> elimination of balancing; see JDK-8202328.)  So I'm taking that bit out.
> 
> New webrevs:
> full: http://cr.openjdk.java.net/~kbarrett/8203319/open.01/
> incr: http://cr.openjdk.java.net/~kbarrett/8203319/open.01.inc/
Still good.