[Qemu-devel] A question about QEMU performance

[Qemu-devel] A question about QEMU performance

[Alessandro Corradi]

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Hi all,
This is my question:
If I run qemu for i386 without kqemu it uses soft-mmu, so it operates as
another architetture as ppc or mips right?
So... are the performace of qemu the same if I use i386 or mips or something
change deeply?
Example: if I run the same program on i386 emulation without kqemu or on
mips are the performance circa the same?

Thanks

Ale

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Re: [Qemu-devel] A question about QEMU performance

[Ben Taylor]

---- Alessandro Corradi <ale.corradi@gmail.com> wrote: 
> Hi all,
> This is my question:
> If I run qemu for i386 without kqemu it uses soft-mmu, so it operates as
> another architetture as ppc or mips right?
> So... are the performace of qemu the same if I use i386 or mips or something
> change deeply?
> Example: if I run the same program on i386 emulation without kqemu or on
> mips are the performance circa the same?

Would you expect qemu to perform the same on an AMD 4600X2 as
a 400 Mhz MIPS?

It's probably all relative to the speed of the cpu, host OS, compiler 
optimizations and trans cpu data transforms, as to how well the 
emulated  system performs.

Re: [Qemu-devel] A question about QEMU performance

[Martin Guy]

> > If I run qemu for i386 without kqemu it uses soft-mmu, so it operates as
> > another architetture as ppc or mips right?
> > So... are the performace of qemu the same if I use i386 or mips or something
> > change deeply?
> > Example: if I run the same program on i386 emulation without kqemu or on
> > mips are the performance circa the same?
>
> Would you expect qemu to perform the same on an AMD 4600X2 as
> a 400 Mhz MIPS?

There are some statistics at freaknet.org/martin/QEMU for various
types of x86 processor, but giving only BogoMIPS, which are way
overrated.
I presume this is cos QEMU translates the kernel speed test loop once
then runs it as x86 code, while "real" tasks need to be translated all
the time.

The only concrete figures I have are from when I timed the running of
bash's configure script, which causes a lot of program execution as
well as compiling and running lots of short test programs. The results
are in cluster.aleph1.co.uk/~martin/qemu.html (please ignore the other
garbage on that page!)

    M

Re: [Qemu-devel] A question about QEMU performance

[Martin Guy]

> There are some statistics at freaknet.org/martin/QEMU for various
> are in cluster.aleph1.co.uk/~martin/qemu.html (please ignore the other

Sorry, that first page is bogus. I meant the second.

    M

Re: [Qemu-devel] A question about QEMU performance

[Rob Landley]

On Wednesday 27 September 2006 4:27 am, Martin Guy wrote:
> There are some statistics at freaknet.org/martin/QEMU for various
> types of x86 processor, but giving only BogoMIPS, which are way
> overrated.
> I presume this is cos QEMU translates the kernel speed test loop once
> then runs it as x86 code, while "real" tasks need to be translated all
> the time.

There is a cache of translated pages, and last I checked (0.8.0 or so) the 
entire translation cache was flushed when it filled up, rather than trying to 
do any kind of LRU-style thing.

I think of qemu as a processor with a bigger than normal penalty for faulting 
executable pages from DRAM into L2. :)

Rob
-- 
"Perfection is reached, not when there is no longer anything to add, but
when there is no longer anything to take away." - Antoine de Saint-Exupery