RFR 8231264: Disable biased-locking and deprecate all flags related to biased-locking

[Andrew Haley]

On 11/27/19 9:08 PM, David Holmes wrote:
> SPECjbb2015 was used as supporting evidence that a modern benchmark
> that people like to measure and report is not impacted by this
> change. As I now know there is a good reason for that. But if
> SPECjbb2015 is somehow supposed to be representative of some class
> of real applications then this also bodes well for those
> applications.

I completely agree.


However, so far we know that:

When uncontended, biased locking is almost an order of magnitude
faster than un-biased locking.

In a couple of benchmarks which use uncontended biased locking, the
performance advantage it brings is 3% - 5%.

ReentrantLocks are about the same speed as un-biased synchronized blocks.

Another claim -- which I make without any evidence -- is that there is
a lot of old Java code out there.


Like many others i would love to be rid of biased locking, and I am
perpetually disappointed by how effective it is.

-- 
Andrew Haley  (he/him)
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
https://keybase.io/andrewhaley
EAC8 43EB D3EF DB98 CC77 2FAD A5CD 6035 332F A671