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Re: [Qemu-devel] [PATCH v2 0/6] target-i386: Make most CPU models work w
From: |
Eduardo Habkost |
Subject: |
Re: [Qemu-devel] [PATCH v2 0/6] target-i386: Make most CPU models work with "enforce" out of the box |
Date: |
Wed, 27 Aug 2014 12:42:13 -0300 |
User-agent: |
Mutt/1.5.23 (2014-03-12) |
On Wed, Aug 27, 2014 at 04:33:54PM +0200, Paolo Bonzini wrote:
> Il 27/08/2014 16:05, Eduardo Habkost ha scritto:
> > On Wed, Aug 27, 2014 at 03:36:51PM +0200, Paolo Bonzini wrote:
> >> Il 26/08/2014 20:01, Eduardo Habkost ha scritto:
> >>> So maybe that's good news, as things can be simpler if we make both TCG
> >>> and KVM have similar behavior:
> >>>
> >>> * qemu64: a conservative default that should work out of the box on
> >>> most systems, for both TCG and KVM. That's already the current status,
> >>> we just need to document it.
> >>>
> >>> * -cpu host: for people who want every possible feature to be enabled
> >>> (but without cross-version live-migration support). We can easily add
> >>> support for "-cpu host" to TCG, too.
> >>
> >> This means that "-cpu host" has different meanings in KVM and TCG. Is
> >> that an advantage or a disadvantage?
> >
> > It is the same meaning to me: "enable everything that's possible,
> > considering what's provided by the underlying accelerator". The "host"
> > name is misleading, though, because on KVM it is close to the host CPU,
> > but on TCG it depends solely on TCG's capabilities.
>
> True. It's not very intuitive, but it is the same concept for processor
> capabilities.
>
> Though for some leaves that do not correspond to processor capabilities,
> "-cpu host" does set them to the host values. This is not just the
> cache model, but also the family/model/stepping/vendor.
>
> For the TCG case, when running on a Nehalem it would be weird to see a
> Nehalem guest with SMAP or ADOX support... I'm not sure it would even
> work to have SVM with an Intel vendor. :)
In that case, the best family/model/stepping/vendor choice depends on
TCG capabilities (defined at compile time), not on the host CPU.
...and that proves your point: if we aren't even using the host CPU
family/model/stepping, calling it "-cpu host" doesn't make much sense.
If it is so different from the host model, we can call it "qemu64" (and
do as you suggests below).
>
> >> If I have to choose blindly, I'd rather give different (but sane)
> >> meanings to "-cpu qemu64" and the same meanings to "-cpu host"...
> >> Basically "-cpu qemu32/64" on KVM would be changed automatically to
> >> kvm32/64.
> >
> > This (different meanings to qemu64) is what I was proposing first,
>
> Good.
>
> > except for the "same meaning to -cpu host" part. What exactly would you
> > expect "-cpu host" to mean on TCG?
>
> Emulate (as much as possible of) a SandyBridge if I'm running on a
> SandyBridge, etc.
>
> "-cpu qemu64" would be the best CPU that TCG can do, with a standard
> family/model/stepping/vendor slapped on top.
Makes sense to me.
--
Eduardo
- [Qemu-devel] [PATCH v2 3/6] target-i386: Disable CPUID_ACPI by default on KVM mode, (continued)
- [Qemu-devel] [PATCH v2 3/6] target-i386: Disable CPUID_ACPI by default on KVM mode, Eduardo Habkost, 2014/08/25
- [Qemu-devel] [PATCH v2 4/6] target-i386: Remove unsupported bits from all CPU models, Eduardo Habkost, 2014/08/25
- [Qemu-devel] [PATCH v2 2/6] target-i386: Rename KVM auto-feature-enable compat function, Eduardo Habkost, 2014/08/25
- [Qemu-devel] [PATCH v2 5/6] target-i386: Don't enable nested VMX by default, Eduardo Habkost, 2014/08/25
- [Qemu-devel] [PATCH v2 6/6] target-i386: Disable SVM by default in KVM mode, Eduardo Habkost, 2014/08/25
- Re: [Qemu-devel] [PATCH v2 0/6] target-i386: Make most CPU models work with "enforce" out of the box, Paolo Bonzini, 2014/08/26
- Re: [Qemu-devel] [PATCH v2 0/6] target-i386: Make most CPU models work with "enforce" out of the box, Eduardo Habkost, 2014/08/26
- Re: [Qemu-devel] [PATCH v2 0/6] target-i386: Make most CPU models work with "enforce" out of the box, Paolo Bonzini, 2014/08/27
- Re: [Qemu-devel] [PATCH v2 0/6] target-i386: Make most CPU models work with "enforce" out of the box, Eduardo Habkost, 2014/08/27
- Re: [Qemu-devel] [PATCH v2 0/6] target-i386: Make most CPU models work with "enforce" out of the box, Paolo Bonzini, 2014/08/27
- Re: [Qemu-devel] [PATCH v2 0/6] target-i386: Make most CPU models work with "enforce" out of the box,
Eduardo Habkost <=
- Re: [Qemu-devel] [PATCH v2 0/6] target-i386: Make most CPU models work with "enforce" out of the box, Andreas Färber, 2014/08/27
- Re: [Qemu-devel] [PATCH v2 0/6] target-i386: Make most CPU models work with "enforce" out of the box, Eduardo Habkost, 2014/08/27
- Re: [Qemu-devel] [PATCH v2 0/6] target-i386: Make most CPU models work with "enforce" out of the box, Andreas Färber, 2014/08/27
- Re: [Qemu-devel] [PATCH v2 0/6] target-i386: Make most CPU models work with "enforce" out of the box, Paolo Bonzini, 2014/08/27
- Re: [Qemu-devel] [PATCH v2 0/6] target-i386: Make most CPU models work with "enforce" out of the box, Eduardo Habkost, 2014/08/27