Improving the performance of OpenJDK

[Andrew Haley]

Gary Benson wrote:
> Andrew Haley wrote:
>> Gary Benson wrote:
>>> So this way around it's a little more encouraging; two of the
>>> times are 8-10% faster, one is 5% faster.  Some of the times are
>>> still slower though, though not by as much, maybe 1-2%.  It's
>>> still disturbingly ambiguous though... thoughts?
>> Big test runs like SPECjvm98 are too coarse for this kind of thing.
> 
> Is there something else I could try instead?  I was thinking about
> trying it with DaCapo tomorrow, that's a little more real-world IMO.

I would have thought DaCapo even worse for looking at this micro-
optimization.  Embedded CaffieneMark was great for this, but isn't
used much these days because it's so small people can cheat.  :-)

>> It's petty unbelievable that with the original get_native_u2() and
>> the new, definitely faster, get_Java_u2() anything can actually get
>> slower.  I'd bet you're looking at noise.  1-2% is vey hard to
>> measure reliably on a multi-user system.
> 
> True.  I'm just wary of declaring it "definitely faster" if, when
> measured, it isn't obviously so.  It may be that the optimization of
> doing aligned loads 50% of the time and then swapping is actually
> faster than reading the bytes individually...

Hard to say.  The real way to find out is to write a test that *only*
does this thing.

Andrew.