|Chris Condrat on Sat, 25 Mar 2006 09:14:44 +0100|
[Date Prev] [Date Next] [Thread Prev] [Thread Next] [Date Index] [Thread Index]
|Re: MPQS behavior|
On 3/24/06, Justin C. Walker <firstname.lastname@example.org> wrote: > For various reasons, I decided to compare my G5 PowerMac and my Core > Duo MacBook Pro in the following computation: I computed the > coefficients of> At this point, the PowerPC has been chewing on this for roughly twice > as long as the Core Duo (the Core Duo has been sleeping a lot :-}). > However, the PowerPC is up to n=193, while the Core Duo is up to n=204. I think you have some misconceptions about the G5 processor. It not even close to equivalent to the performance of the Core Duo. With few exceptions, only applications which are not Universal Binaries (UB) perform worse on a Core Duo compared to a G5 (http://www.barefeats.com/). If you compiled PARI on the laptop, it was compiled for native code, making it extremely fast, and I would guess that your Macbook Pro, and the Core iMac, should you buy one, would both perform better than your G5. Apple was smart to bail on the G5, because it was fast becoming forgettable. For PARI, the performance loss on the G5 was probably exacerbated by other problems as well. For instance, the G5 is a 64-bit processor, and if the binaries were compiled in 64-bit mode, they are nearly always slower than the 32-bit equivalent (and the Core Duo is a 32-bit processor). Even if the Core Duo's potentially hidden EMT64 instructions were enabled, the Core Duo would gain performance as the x86 is one of the only processors which derives benefit from 64-bit instructions due to additional registers. Type "precision(x)" in GP if you want to see how many bits PARI was compiled for (2^31 is the 32-bit). Apple also chose to go the way of parallelism with its G5 machines because of scalability problems with G5 processors from IBM, and PARI is not designed with parallelism in mind. Finally, many apps on the G5 only performed well because they were optimized for the AltVec units. PARI does not support such SIMD instructions as far as I know.