[aarch64-port-dev ] RFR: 8217368: AArch64: C2 recursive stack locking optimisation not triggered

[Andrew Haley]

Hi,

On 1/22/19 9:10 AM, Nick Gasson (Arm Technology China) wrote:
> 
> Please see the updated webrev to use cmpxchg in both the lock and unlock 
> functions:
> 
> http://cr.openjdk.java.net/~ngasson/8217368/webrev.1/
> 
> Also includes Derek's cleanup suggestions (although some of them are not 
> applicable now).
> 
> Testing I've done on this:
> 
> * Ran jtreg with assertions enabled (+UseLSE)
> 
> * Ran jcstress with both +UseLSE and -UseLSE
> 
> * Ran the JMH LockUnlock benchmarks with -UseBiasedLocking to check for 
> performance regressions.
> 
> The directory below contains the the generated assembly from each webrev 
> and current hg tip for this simple method:
> 
> http://cr.openjdk.java.net/~ngasson/8217368/generated/

Excellent, thanks for that. Otherwise I'd have had to generate these myself.

>      private Object obj = new Object();
>      public int x;
> 
>      private void incX() {
>          synchronized (obj) {
>              x++;
>          }
>      }
> 
> The output of webrev.1 looks OK to me. Any other suggestions of things 
> to test?

That looks right, thanks. It's extremely difficult to test this stuff in practice.
Does any of the above stress test  recursive locking in the presence of many threads?

-- 
Andrew Haley
Java Platform Lead Engineer
Red Hat UK Ltd. <https://www.redhat.com>
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