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[Qemu-devel] is the "tcg translation" necessary when the "kvm accelerati


From: tugouxp
Subject: [Qemu-devel] is the "tcg translation" necessary when the "kvm acceleration" emulation mode enabled?
Date: Fri, 21 Dec 2018 09:57:47 +0800 (CST)

hi folks:
    i am very puzzled about the relationship between "target cpu instruction"  
translated to host instructions through TCG module and the "kvm" acceleration" 
mode.


think about three scenario of emulation:
scenario 1, 2 and 3 as follows:

1. target cpu: x86_64,

    host cpu:   x84_64,

    emulation OS:   ubuntu_desktop_amd64.iso
    kvm:  enabled.


2. target cpu: x86_64,

    host cpu:   x84_64,

    emulation OS:   ubuntu_desktop_amd64.iso
    kvm:  disabled.


3. target cpu  x86_64,
    host cpu:  armv8
    emulationOS: ubuntu_desktop_amd64.iso
    kvm:  enabled


my question is:
scenario 1:  did the tcg translation need to be done in this case now that the 
host and target arch is the same?  or  let the kvm emulation the system wit the 
original instructions with out the TCG   translation´╝č
scenario 2:   the pre condition is same with scenario 1 except the kvm is 
disable´╝č so ,in this scenario, the TCG must be used in order to the pure 
software emulation without acceleration?
scenario 3:  in this scenario, the host and target arch is not the same, so how 
to use the "kvm mechainsim" in this case?  so the instructions feed to the kvm 
module to run must be translated By TCG module? right?


thanks for your kindly support for my puzzle.



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