Re: Altivec in baseline for ppc64?
On Fri, Jul 16, 2021 at 2:59 AM John Paul Adrian Glaubitz
<glaubitz@physik.fu-berlin.de> wrote:
>
> On 7/15/21 5:49 PM, Christian Zigotzky wrote:
> > I disagree too because the performance of software with AltiVec support isn't as
> > high as expected. I tested it a lot because we have AltiVec and Non-Altivec machines
> > here. We changed to Non-AltiVec compiled software a while ago.
>
> 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.
+1
I've found a few algorithms that were profitable on ARM and x86, but
not profitable with Altivec. The LEA algorithm comes to mind:
https://github.com/weidai11/cryptopp/blob/master/lea_simd.cpp#L46.
Altivec runs about 5x slower than C++.
> > We and the MintPPC team had some problems with the VLC media player on our Non-AltiVec
> > machines a year ago because it is only available in an AltiVec version.
> > The MintPPC team had to recompile it. [1]
> > We also had to recompile the version 3.0.12 of VLC because of the AltiVec dependency again. [2]
>
> 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.
Does it have to be one or the other? Can't you have both?
Jeff
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