[10] RFR(S): 8185572: Enable AssumeMP by default on SPARC machines

[Vladimir Kozlov]

CCing to Runtime.

Can you add comment explaining why it set to true on SPARC?

Thanks,
Vladimir

On 8/10/17 6:26 AM, Poonam Parhar wrote:
> Hello,
> 
> Please review this simple patch:
> 
> Bug:_JDK-8185572_<https://bugs.openjdk.java.net/browse/JDK-8185572>:Enable 
> AssumeMP by default on SPARC machines
> 
> Webrev:http://cr.openjdk.java.net/~poonam/8185572/webrev.00/
> 
> This change enables AssumeMP by default on SPARC machines. On Sparc T7, 
> to finalize BIS instructions the server compiler needs toadd 
> a‘membar’instruction at the end.But the generation of‘membar’is guarded 
> byos::is_MP(), andos::is_MP()returns false when there isa singlecpu 
> available on the system. Now,invirtualized/containerenvironments, the 
> number ofprocessorsallocated to a virtual machine can dynamically change 
> during the application runtime.That could lead to incorrect generation 
> of BIS instructions and can cause JVM crashes.Enabling AssumeMP makes 
> is_MP() always return true on SPARC systems.
> 
> In future, we may consider makinggeneration of‘membar‘unconditional 
> withtheenhancementrequest:_JDK-8150715_<https://bugs.openjdk.java.net/browse/JDK-8150715>.
> 
> Thanks,
> 
> Poonam
>