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

From: Alexander Graf
Subject: Re: [Qemu-devel] [PATCH] OSX x86_32 host support
Date: Tue, 15 Jan 2008 18:50:41 +0100

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. ;-)



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