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