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Re: [Qemu-devel] is the "tcg translation" necessary when the "kvm accele


From: tugouxp
Subject: Re: [Qemu-devel] is the "tcg translation" necessary when the "kvm acceleration" emulation mode enabled?
Date: Fri, 21 Dec 2018 16:00:49 +0800 (CST)

much appreciate!

:)








At 2018-12-21 14:33:08, "Paolo Bonzini" <address@hidden> wrote:
>> 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
>
>TCG is turned off when KVM is enabled.  The code for TCG does not run at
>all.
>
>> scenario 2:   the pre condition is same with scenario 1 except the kvm
>> is disableļ¼Ÿ so ,in this scenario, the TCG must be used in order to
>> the pure software emulation without acceleration?
>
>Correct.  In this case KVM is turned off.  The capabilities of the
>emulated CPU will _not_ be what you have in your host processor, but
>rather what QEMU implements.  For example, you will get no AVX.
>
>> 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?
>
>KVM cannot be used in this case; KVM is only enabled when the host and
>the target are the same.
>
>Paolo
>
>On 21/12/18 02:57, tugouxp wrote:
>> 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

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