[Qemu-devel] how to get the features of a cpu model

[Feng, Shaohe]

Hi all, 

I write a script to get the features of a cpu model

https://github.com/shaohef/cpu_model_features/blob/master/intersection_features.py

I use “qemu -cpu model,+features,check“ to try whether  a cpu model can support 
a  feature.

I find different cpu models can support same features on same host.
such as a result on one of my host with ivybridge CPU.

model: n270
    support 55 featurs: ['kvmclock', 'pge', 'avx', 'clflush', 'sep', 'syscall', 
'tsc-deadline', 'kvm_pv_eoi', 'fsgsbase', 'xsave', 'msr', 'vmx', 
'kvm_pv_unhalt', 'erms', 'cmov', 'f16c', 'smep', 'ssse3', 'tsc', 'fxsr', 'pae', 
'mce', 'vme', 'mmx', 'cx8', 'rdtscp', 'mca', 'pse', 'popcnt', 'apic', 'sse', 
'pat', 'kvm_steal_time', 'kvm_asyncpf', 'lahf_lm', 'aes', 'sse2', 'ss', 
'hypervisor', 'pcid', 'de', 'fpu', 'cx16', 'pse36', 'mtrr', 'rdrand', 
'kvm_nopiodelay', 'x2apic', 'sse4.2|sse4_2', 'sse4.1|sse4_1', 
'pclmulqdq|pclmuldq', 'pni|sse3', 'lm|i64', 'fxsr_opt|ffxsr', 'nx|xd']

================================================================================
model: Conroe
    support 55 featurs: ['kvmclock', 'pge', 'avx', 'clflush', 'sep', 'syscall', 
'tsc-deadline', 'kvm_pv_eoi', 'fsgsbase', 'xsave', 'msr', 'vmx', 
'kvm_pv_unhalt', 'erms', 'cmov', 'f16c', 'smep', 'ssse3', 'tsc', 'fxsr', 'pae', 
'mce', 'vme', 'mmx', 'cx8', 'rdtscp', 'mca', 'pse', 'popcnt', 'apic', 'sse', 
'pat', 'kvm_steal_time', 'kvm_asyncpf', 'lahf_lm', 'aes', 'sse2', 'ss', 
'hypervisor', 'pcid', 'de', 'fpu', 'cx16', 'pse36', 'mtrr', 'rdrand', 
'kvm_nopiodelay', 'x2apic', 'sse4.2|sse4_2', 'sse4.1|sse4_1', 
'pclmulqdq|pclmuldq', 'pni|sse3', 'lm|i64', 'fxsr_opt|ffxsr', 'nx|xd']

================================================================================
model: SandyBridge
    support 55 featurs: ['kvmclock', 'pge', 'avx', 'clflush', 'sep', 'syscall', 
'tsc-deadline', 'kvm_pv_eoi', 'fsgsbase', 'xsave', 'msr', 'vmx', 
'kvm_pv_unhalt', 'erms', 'cmov', 'f16c', 'smep', 'ssse3', 'tsc', 'fxsr', 'pae', 
'mce', 'vme', 'mmx', 'cx8', 'rdtscp', 'mca', 'pse', 'popcnt', 'apic', 'sse', 
'pat', 'kvm_steal_time', 'kvm_asyncpf', 'lahf_lm', 'aes', 'sse2', 'ss', 
'hypervisor', 'pcid', 'de', 'fpu', 'cx16', 'pse36', 'mtrr', 'rdrand', 
'kvm_nopiodelay', 'x2apic', 'sse4.2|sse4_2', 'sse4.1|sse4_1', 
'pclmulqdq|pclmuldq', 'pni|sse3', 'lm|i64', 'fxsr_opt|ffxsr', 'nx|xd’]

you can see there is  no difference for the supported features between n270, 
SandyBridge.


Also I have get a result on another host with haswell CPU.

================================================================================
model: SandyBridge
    support 65 featurs: ['kvmclock', 'pge', 'avx', 'clflush', 'sep', 'rtm', 
'tsc-deadline', 'abm', 'fsgsbase', 'xsave', 'msr', 'vmx', 'kvm_pv_unhalt', 
'erms', 'hle', 'cmov', 'f16c', 'smep', 'ssse3', 'tsc', 'fxsr', 'syscall', 
'pae', 'mce', 'fma', 'vme', 'mmx', 'cx8', 'rdtscp', 'mca', 'pse', 'popcnt', 
'invpcid', 'pdpe1gb', 'apic', 'sse', 'pat', 'kvm_steal_time', 'kvm_pv_eoi', 
'kvm_asyncpf', 'lahf_lm', 'aes', 'avx2', 'sse2', 'ss', 'hypervisor', 'bmi1', 
'bmi2', 'pcid', 'de', 'fpu', 'cx16', 'pse36', 'mtrr', 'movbe', 'rdrand', 
'kvm_nopiodelay', 'x2apic', 'sse4.2|sse4_2', 'sse4.1|sse4_1', 
'pclmulqdq|pclmuldq', 'pni|sse3', 'lm|i64', 'fxsr_opt|ffxsr', 'nx|xd’]


You can see the same CPU model SandyBridge can support more features on the 
host with haswell CPU than the host with ivybridge CPU.



My questions are:
1. can I live-migration the vm with same  CPU model(for example SandyBridge)  
between  haswell host and ivybridge host 
2. does qemu support a API to get it’s emulated CPUID?