x86: 0.875
performance: 0.813
graphic: 0.777
mistranslation: 0.587
device: 0.536
semantic: 0.518
files: 0.501
architecture: 0.424
i386: 0.406
socket: 0.358
boot: 0.318
network: 0.311
vnc: 0.239
permissions: 0.226
virtual: 0.222
ppc: 0.219
user-level: 0.206
register: 0.192
PID: 0.162
peripherals: 0.129
kernel: 0.128
debug: 0.122
risc-v: 0.120
VMM: 0.112
hypervisor: 0.106
arm: 0.104
assembly: 0.104
TCG: 0.074
KVM: 0.033

qemu-system-x86_64 version 3.0+ is 20 times slower than version 2.12

version 3.0+ is 20 times slower than version 2.12
I wrote a small 64-bit operating system (SIGMAOS) in which I use the lzma decoder. unpacking the file takes 20 times slower than in version 2.12.
You can download it from https://drive.google.com/drive/folders/0B_wEiYjzVkC0ZGtkbENENzF1Nms

Your linked drive doesn't seem to have any readme or documentation for how this is invoked. Please see:

  https://www.qemu.org/contribute/report-a-bug/

Specifically the host/guest details and the full command line that you have used to run this binary. 

As developers may be wary about running on unknown binary on their systems you may find it quicker to do some experiments yourself. If you run qemu under perf for 2.12 and 3.0+ (or current git) that might give some indication about what has changed.

[Expired for QEMU because there has been no activity for 60 days.]