Re: [Qemu-devel] [PATCH] OSX x86_32 host support

[Alexander Graf]

On Jan 15, 2008, at 6:30 PM, Andreas Färber wrote:

> Am 15.01.2008 um 17:32 schrieb Alexander Graf:
>
> > Jamie Lokier wrote:
> > > Alexander Graf wrote:
> > >
> > > > I believe the 5% performance hit
> > > > that goes with them is no real problem, as most people should be  
> > > > using
> > > > x86_64 nowadays anyway.
> > >
> > > *Boggle*!  x86_64 is only a few years old, and cheap low-power  
> > > x86_64
> > > laptops are relatively recent.
> > >
> > > -- Jamie
> > So you really want to do dynamic retranslation on ancient hardware?  
> > To
> > me emulated systems already feel slow on really recent machines, I
> > don't  want to go back to something even slower.
> > If you use kqemu there even is near no performance hit at all,  
> > which I
> > believe is the main use of qemu on i386 anyway. Furthermore x86_64 is
> > _way_ faster, as it provides a lot more registers.
> >
> > I think the benefit you get from cutting the gcc3 dependency is way  
> > more
> > important than a major performance hit that people will usually  
> > only see
> > on the next release of qemu, by which time things have shifted  
> > towards
> > x86_64 even more.
>
> One thing you don't seem to understand is that QEMU releases don't  
> upgrade our hardware, especially not from Apple. An x86_64 Mac Pro  
> is more than double the price for my PowerMac G5 back then. Don't  
> think about what people "should" be using in your opinion, look at  
> what they are actually using.

What I am actually talking about is that the only real gcc4 breakage I  
am aware of is on i386. I just built x86_64-softmmu on a POWER6 host  
with gcc4.1.2 and it "simply worked". Please tell me if there is  
anything broken for you on gcc4. I believe there isn't (please use  
gcc4.2+).

> People want to run software, including Q or QEMU, on their hard- and  
> software, which may include ppc hardware as well as Panther/Tiger  
> operating systems ... both much more "ancient" than Intel Core 2 Duo  
> based Macs. And yes, it's "slow". Does that stop me? No. And you  
> likely don't have a kqemu on your Mac either. Occasionally trying an  
> image does not justify buying VMware Fusion, and such commercial  
> products only do virtualization anyway and are incapable of  
> emulating different hardware. Just in case you forgot, Open Source  
> software in general usually has the benefit of not being tied to the  
> support lifetimes of commercial vendors, forcing users to upgrade  
> their (e.g. Windows) OS - but pushing us to upgrade our hardware as  
> soon as something faster is out would be doing exactly that hardware- 
> wise, without substantial reason.

I wasn't talking about PowerPC. I am really sorry if it looked that  
way, but it was neither my intention nor my belief to say anything  
against any platform but i386.

> As a user, I don't want to do dynamic retranslation. I still don't  
> really understand how it works (seems more complicated than the JIT  
> I'm working with). I just want to emulate a machine in my preferred  
> environment, especially ppc64 and sparc64 targets for work on Open  
> Source software. QEMU is the only emulator I know that is on its way  
> there.
>
> Flame me if you need to, but please stop this "everyone is using  
> x86_64 anyway" argument; if you have improvements specific to that  
> host, simply make them conditional, that's what configure is for.

I was saying "let's finally make qemu gcc4-save, so we can drop this  
gcc3 dependency. The only platform that might get a performance hit  
from that is i386 and I was trying to show why a small performance hit  
on i386 is no real problem if we can use gcc4 for every target instead.

> With the gcc3 part I do agree.

Thank you. ;-)

Regards,

Alex