Re: [Qemu-devel] Re: branches are expensive

[Laurent Desnogues <laurent.desnogues@gmail.com>]

On Thu, Mar 19, 2009 at 11:39 AM, Steffen Liebergeld <usenet@gmx.eu> wrote:
> 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.

I said "guest" not "host" :)

You need to compare ARM and i386 blocks *before* translation.


Laurent