On Fri, Dec 29, 2023 at 2:10 PM Stefan Hajnoczi <stefa...@gmail.com> wrote:
> > First, performance: since some years ago, since prior to qemu 6.2 until
> > latest 8.2, win10 and win11 vms always worked slower than expected. This
> > could be noticed by comparing booting/starting times between vm and a
> > bare metal installation, but I particularly measured it when installing
> > windows cumulative updates through windows update. On vm, from
> > downloading to finishing rebooting it always took 1.5 circa 1.5 hours,
> > while just 40 minutes on bare metal.
One possibility is that you have Hyper-V enabled with -cpu host but
not with other CPU models. That's because "-cpu host" enables nested
virtualization.
Try "-cpu host,-vmx" and it should be clear if that's the case.
Based on the pastie that you prepared, that's the main difference
between -cpu host and -cpu Broadwell-noTSX-IBRS. Nothing else (see
list below) should have any substantial performance impact; even less
so should they make things worse.
Paolo
"avx512-vp2intersect": true,
"avx512-vpopcntdq": true,
"avx512bitalg": true,
"avx512bw": true,
"avx512cd": true,
"avx512dq": true,
"avx512f": true,
"avx512ifma": true,
"avx512vbmi": true,
"avx512vbmi2": true,
"avx512vl": true,
"avx512vnni": true,
"full-width-write": true,
"gfni": true,
"vaes": true,
"vpclmulqdq": true,
"clflushopt": true,
"clwb": true,
"fsrm": true,
"host-cache-info": false,
"host-phys-bits": true,
"amd-ssbd": true,
"amd-stibp": true,
"arch-capabilities": true,
"ibpb": true,
"ibrs": true,
"ibrs-all": true,
"ssbd": true,
"stibp": true,
"kvm-pv-ipi": true,
"kvm-pv-sched-yield": true,
"kvm-pv-tlb-flush": true,
"kvm-pv-unhalt": true,
"lmce": true,
"md-clear": true,
"mds-no": true,
"movdir64b": true,
"movdiri": true,
"pdcm": true,
"pdpe1gb": true,
"pdcm": false,
"pdpe1gb": false,
"pku": true,
"pmu": true,
"pschange-mc-no": true,
"rdctl-no": true,
"rdpid": true,
"sha-ni": true,
"ss": true,
"tsc-adjust": true,
"umip": true,
"vmx": true,
"xgetbv1": true,
"xsavec": true,
"xsaves": true,
(skipped everything vmx-related, since they don't matter with vmx
itself being false)
