[Qemu-devel] Re: branches are expensive

[Steffen Liebergeld <usenet@gmx.eu>]

Laurent Desnogues <laurent.desnogues@gmail.com> schrieb:
> On Thu, Mar 19, 2009 at 11:07 AM, Steffen Liebergeld <usenet@gmx.eu> wrote:
>>
>> I've tested Qemu 0.10.0 and with i386-softmmu on a i386 host I get the
>> following numbers:
>> direct jump count 70%, 2 jumps 54%
>>
>> For qemu-system-arm on an ARM host, the numbers look like this:
>> direct jump count 47%, 2 jumps 40%
>>
>> For completeness I tested qemu-system-arm on a i386 host as well:
>> direct jump count 44%, 2 jumps 37%
>>
>> So it looks like the chaining on ARM targets is not as effective as on i386
>> targets (regardless of the guest, I used the same guest setup, compiled for
>> different architectures, on all tests). Do you have any ideas why this is the
>> case?
>
> Different instruction sets, different compilers.  You'd better compare
> guest code before drawing any conclusion.

The qemu-system-arm on ARM and i386 were compiled by the same compiler.

Greetings, Steffen