Improving the performance of OpenJDK
gbenson at redhat.com
Thu Feb 19 09:43:46 PST 2009
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.
> 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...
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