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performance: 0.801
graphic: 0.774
KVM: 0.731
architecture: 0.704
x86: 0.571
device: 0.568
hypervisor: 0.479
network: 0.455
files: 0.434
PID: 0.394
kernel: 0.372
vnc: 0.328
semantic: 0.319
ppc: 0.316
socket: 0.287
permissions: 0.272
user-level: 0.266
debug: 0.249
boot: 0.237
virtual: 0.227
risc-v: 0.215
VMM: 0.201
register: 0.200
TCG: 0.194
peripherals: 0.142
arm: 0.131
i386: 0.119
mistranslation: 0.088
assembly: 0.068
Emulated newer x86 chipsets are noticably slower on cpu-bound loads than "-cpu qemu64"
Description of problem:
I noticed that "-cpu qemu64" is much faster than "-cpu max" or "-cpu Icelake-Server-noTSX" for cpu bound loads, and with more than one cpu under load.
Steps to reproduce:
1. Run a guest as per "qemu-system-x86_64 -cpu max [..]" command from above. Any linux distro should do.
2. run through the setup questions if you use Fedora-Server-KVM-41-1.4.x86_64.qcow2 from the example command line above
3. log into the guest via ssh, i.e. "ssh chris@amd64" here
4. cd /dev/shm; wget http://archive.apache.org/dist/httpd/httpd-2.4.57.tar.bz2; wget https://fluxcoil.net/files/tmp/job_httpd_extract_cpu.sh
6. bash ./job_httpd_extract_cpu.sh 4 300
8. cat /tmp/counter
Step 6 is executing a script which simply uses 4 parallel loops, where each loop runs "bzcat httpd-2.4.57.tar.bz2" constantly. After 300sec, the successful uncompressions over all 4 loops are summed up and stored in /tmp/counter.
- result with "-cpu qemu64": 96
- result with "-cpu max": 84
- result with "-cpu Icelake-Server-noTSX": 44
Additional information:
- For "-cpu Icelake-Server-noTSX" on this Thinkpad T590 I get these warnings, I think they are not relevant:
qemu-system-x86_64: warning: TCG doesn't support requested feature: CPUID.01H:ECX.pcid [bit 17]
qemu-system-x86_64: warning: TCG doesn't support requested feature: CPUID.01H:ECX.tsc-deadline [bit 24]
[..]
- I also looked at Broadwell etc, and all of them seem in the same ballpark.
Graph over some emulated architectures: https://fluxcoil.net/files/tmp/gnuplot_cpu-performance-emulated-only.png
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