F 15. 64 bit versus 32 bit.

[Andrew Haley]

On 05/24/2011 05:57 PM, Fernando Cassia wrote:
> On Tue, May 24, 2011 at 13:47, Andrew Haley <aph at redhat.com> wrote:
>> Ever since
>> Compressed OOPs became the default there's no big advantage to running
>> 32-bit Java, at least on HotSpot.
> 
> ----
> What are the performance characteristics of 64-bit versus 32-bit VMs?
> 
> Generally, the benefits of being able to address larger amounts of
> memory come with a small performance loss in 64-bit VMs versus running
> the same application on a 32-bit VM.  This is due to the fact that
> every native pointer in the system takes up 8 bytes instead of 4.

But because of Compressed OOPs that's no longer true, and you get
the advantage of

> ... some additional registers which it can use to generate
> more efficient native instruction sequences.  These extra registers
> increase performance to the point where there is often no performance
> loss at all when comparing 32 to 64-bit execution speed.

and you also get the advantage of longs fitting in a register.

Andrew.