Re: [Qemu-ppc] [Qemu-devel] [PATCH v3 2/8] target/ppc: rework vmrg{l, h}{b, h, w} instructions to use Vsr* macros

[BALATON Zoltan]

On Sun, 27 Jan 2019, BALATON Zoltan wrote:
> On Sun, 27 Jan 2019, Mark Cave-Ayland wrote:
> > On 27/01/2019 17:26, Richard Henderson wrote:
> >
> > > On 1/27/19 7:19 AM, Mark Cave-Ayland wrote:
> > > > Could this make the loop slower? I certainly haven't noticed any obvious
> > > > performance difference during testing (OS X uses merge quite a bit for
> > > > display rendering), and I'd hope that with a good compiler and modern 
> > > > branch
> > > > prediction then any effect here would be negligible.
> > >
> > > I would expect the i < n/2 loop to be faster, because the assignments are
> > > unconditional.  FWIW.
> >
> > Do you have any idea as to how much faster? Is it something that would show 
> > up as
> > significant within the context of QEMU?
>
> I don't have numbers either but since these vector ops are meant to and are 
> used for speeding up repetitive calculations I'd expect it to be run many 
> times which means that even a small difference would add up. So I think it's 
> worth trying to make these optimal also when host vector ops cannot be used.
>
> I don't know about a good benchmark to measure this. Maybe you could try 
> converting some video in Mac OS X or something similar that's known to use 
> AltiVec/VMX. There are also these under MorphOS on mac99:
> http://www.amiga-news.de/en/news/AN-2012-02-00011-EN.html
> where the mplayer one is mostly VMX bound I think and lame is more dependent 
> on floating point ops but that also has a VMX version (still mainly float I 
> think). I'd copy input file to RAM: disk first to avoid overhead from IDE 
> emulation. But these are probably too short to measure this.
>
> I can't test this now but maybe someone reading this on the list who can try 
> it with and without this series could help.

I've found these (untested and quite old but may work) so you don't need 
MorphOS only OS X:

https://tmkk.undo.jp/lame/index_e.html

Regards,
BALATON Zoltan