Re: [Qemu-devel] [PATCH] Enabled building of x86_64 code on Mac OS X

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

On Tue, Jan 27, 2009 at 10:21 AM, Alexander Graf <agraf@suse.de> wrote:
>
> The extra registers should speed up things quite a bit. While that's not
> too much of a problem when emulating x86, which has few registers
> anyway, emulating a ppc or x86_64 target should be faster on an x86_64
> host. I haven't done measurements though.
>
> As for the plus in code size on x86_64 - that doesn't really apply to
> tcg, as that still generates 32-bit code when only 32-bit code is
> necessary, which still looks the same on x86_64. Plus it does simplify
> 64-bit operations.
>
> I would be very surprised if the improvement of emulating x86_64 on x86
> vs. x86_64 is only ~10%.

Here is a quick result for user mode.

x on y means running an target x on host y (the host is the same,
I just forced --cpu=i386 when compiling qemu).

Host:  CentOS 5.2 x86_64, E6600 (2.4GHz)
Benchmark: Spec2k gcc/integrate (compiled with gcc 4.1.2 -O2)

i386 on x86_64
gen code size       4005696/33497088
TB count            30704/524288
real    0m24.983s/user    0m24.834s

x86_64 on x86_64
gen code size       4413408/33497088
TB count            30247/524288
real    0m24.932s/user    0m24.749s

i386 on i386
gen code size       3439008/33497088
TB count            30704/524288
real    0m26.391s/user    0m26.131s

x86_64 on i386
gen code size       5715248/33497088
TB count            30254/524288
real    0m28.233s/user    0m27.985s


Laurent