i386: 0.983
performance: 0.961
x86: 0.950
TCG: 0.913
architecture: 0.895
graphic: 0.856
vnc: 0.835
device: 0.828
kernel: 0.773
ppc: 0.761
boot: 0.755
files: 0.739
VMM: 0.736
register: 0.728
risc-v: 0.705
PID: 0.678
permissions: 0.628
socket: 0.627
arm: 0.626
mistranslation: 0.582
user-level: 0.483
debug: 0.453
semantic: 0.450
virtual: 0.378
KVM: 0.348
hypervisor: 0.300
network: 0.285
assembly: 0.206
peripherals: 0.174

Absolutely slow Windows XP SP3 installation

Host: Linux 4.3.3 vanilla x86-64/Qemu 2.5 i686 (mixed env)
Guest: Windows XP Professional SP3 (i686)

This is my launch string:

$ qemu-system-i386 \
-name "Windows XP Professional SP3" \
-vga std \
-net nic,model=pcnet \
-cpu core2duo \
-smp cores=2 \
-cdrom /tmp/en_winxp_pro_with_sp3_vl.iso \
-hda Windows_XP.qcow \
-boot d \
-net nic \
-net user \
-m 1536 \
-localtime

Console output:

warning: TCG doesn't support requested feature: CPUID.01H:EDX.vme [bit 1]
warning: TCG doesn't support requested feature: CPUID.80000001H:EDX.syscall [bit 11]
warning: TCG doesn't support requested feature: CPUID.80000001H:EDX.lm|i64 [bit 29]
warning: TCG doesn't support requested feature: CPUID.01H:EDX.vme [bit 1]
warning: TCG doesn't support requested feature: CPUID.80000001H:EDX.syscall [bit 11]
warning: TCG doesn't support requested feature: CPUID.80000001H:EDX.lm|i64 [bit 29]

After hitting 35% installation more or less stalls (it actually doesn't but it progresses 1% a minute which is totally unacceptable).

That was without KVM acceleration, so perhaps it's how it's meant to be.

With KVM everything is fast and smooth.

For integer workloads such as installing an OS you should expect TCG to be about 12x slower than KVM on average. That is on current master; note that TCG has gotten faster in the last couple of years. See a performance comparison from v2.7.0 to v2.11.0 for SPEC06 here: https://imgur.com/a/5P5zj

I've therefore marked the report as invalid, as I don't think the aforementioned speedups will change your experience dramatically.