MFENCE vs. LOCK addl

[Paul Hohensee]

Good idea.  Can you try it, Azeem?

Paul

John Rose wrote:
> What about XCHG?  It doesn't set flags, and (as a bonus) it implies 
> the effect of a LOCK prefix:
>     push rax
>     xchg rax
>     pop rax
>
> -- John
>
> On Feb 25, 2009, at 7:05 AM, Jiva, Azeem wrote:
>
>> Paul,
>>  Ahh right, I did some experiments with running MFENCE vs. LOCK ADDL
>> and MFENCE vs. PUSH/LOCK ADDL/POPF and found that MFENCE is faster than
>> PUSH/LOCK/POP but not faster than just using the LOCK instruction by
>> itself.  A nice optimization would be if the JVM could detect if the
>> condition codes needed to be saved instead of saving them always.   This
>> is on AMD hardware, and other systems might have different performance
>> issues.
>