Re: [Qemu-devel] ARM CPU Speed simulated by Qemu?

Re: [Qemu-devel] ARM CPU Speed simulated by Qemu?

[Laurent DESNOGUES]

> Now, CPUs is where I have only a vague idea of what would be needed to 
> simulate. I know there are up to three levels of caches and main memory, 
> which all have different access times. The CPU itself has a pipeline and 
> branch prediction and such which could invalidate the contents of 
> pipeline up to a given point (of branching).
> 
> I think the most time consuming operation which should be properly 
> simulated is memory access. For this to work properly, all levels of 
> caches must be emulated, too.
> 
> How much do misses on the branch prediction level cost? How much 
> pipeline interlocks? I don't think those would be _that_ dramatic. Since 
> today's compilers are said to be optimizing quite well...

The most complex thing to accurately simulate a modern
CPU (including ARMs) is the data cache and by far.  In
comparison, getting accurate core pipeline simulation
is *very* easy.

There is a company that claims to be able to accurately
simulate an at 200 Mhz (http://www.vastsystems.com).  I
bet there are using statistical cycle counting and so
are probably very wrong :)


Laurent

Re: [Qemu-devel] ARM CPU Speed simulated by Qemu?

[Markus Schiltknecht]

Hi,

Laurent DESNOGUES wrote:
> The most complex thing to accurately simulate a modern
> CPU (including ARMs) is the data cache and by far. 

Hm... you have to elaborate on that one. Aren't those caches like other 
caches, too? With well known algorithms like LRU?

> In
> comparison, getting accurate core pipeline simulation
> is *very* easy.

Simulating branch prediction seems more complex to me (probably because 
I'm thinking x86, not ARM).

What to others think about the network and hard disk simulation I've
mention in my previous post?

Regards

Markus

Re: [Qemu-devel] ARM CPU Speed simulated by Qemu?

[K. Richard Pixley]

I have at least one 450Mhz k6 in my spare bedroom.  I'll by happy to 
sell it to you as a platform for running debian and qemu.  I'm sure it's 
performance would be lower than most of the current amd processors, 
though it might not be slower than some of the current intel chips, 
(*grin*).

--rich

[Qemu-devel] Re: ARM CPU Speed simulated by Qemu?

[Antti P Miettinen]

Laurent DESNOGUES <laurent.desnogues@wanadoo.fr> writes:
> There is a company that claims to be able to accurately
> simulate an at 200 Mhz (http://www.vastsystems.com).  I
> bet there are using statistical cycle counting and so
> are probably very wrong :)

Well, their simulation speed depends on the kind of code run and the
kind of models simulated, but their tools are indeed fast, presumably
mostly thanks to dynamic compilation. And at least the core models
seem quite accurate.

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