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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 disable? 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