[Date Prev][Date Next] [Thread Prev][Thread Next] [Date Index] [Thread Index]

Re: Altivec in baseline for ppc64?


John Paul Adrian Glaubitz wrote:
It depends on the workload, of course. Anything that does SIMD like matrix multiplications
in multimedia or scientific computing will, of course, profit from enabling AltiVec.

No one claimed that AltiVec, MMX or SSE will just improve everything.

Exactly, let's clarify something out direct experience. I don't know if things improved recently, but essentiallty GCC some years ago did not do real auto-vectoring. Enabling AltiVec essentially does nothing, it allows you to write code to use it, but it will not magically turn code faster. For specific libraries and applications which do support AltiVec (e.g. many video-decoding or image processing) improvements may be great. Especially on "older" processors like G4 or G5. On intel instead code may be faster with MMX, SSEx because additional resources and registers are opened up (on 32bit).

If also AltiVec can now benefit of auto-vectoring I'm interested to know, I have myself written imaging code and never noticed improvement in AV just by turning it on, but did not retest with recent GCC.

I would argue that there are far more users with PowerMacs which all support AltiVecs than
with obscure embedded machines. As I said, some packages like nss2 already enabled AltiVec
by default.

As far as PowerMacs you are completely right, but PPC is used more and more on "other" systems too, boards done with the available NXP processors and several are based on embedded CPUs, e.g. e5500 cores and variations.
Our upcoming PPC Laptop will have AltiVec, but other not.


Reply to: