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Re: [Qemu-devel] [PATCH 4/6] i386: Infrastructure for versioned CPU mode
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH 4/6] i386: Infrastructure for versioned CPU models |
Date: |
Tue, 25 Jun 2019 15:56:51 +0100 |
User-agent: |
Mutt/1.12.0 (2019-05-25) |
* Eduardo Habkost (address@hidden) wrote:
> On Tue, Jun 25, 2019 at 03:32:16PM +0100, Dr. David Alan Gilbert wrote:
> > * Eduardo Habkost (address@hidden) wrote:
> > > On Tue, Jun 25, 2019 at 10:32:01AM +0100, Dr. David Alan Gilbert wrote:
> > > > * Eduardo Habkost (address@hidden) wrote:
> > > > > Base code for versioned CPU models. This will register a "-4.1"
> > > > > version of all existing CPU models, and make the unversioned CPU
> > > > > models be an alias for the -4.1 versions on the pc-*-4.1 machine
> > > > > types.
> > > > >
> > > > > On older machine types, the unversioned CPU models will keep the
> > > > > old behavior. This way, management software can use old machine
> > > > > types while resolving aliases if compatibility with older QEMU
> > > > > versions is required.
> > > > >
> > > > > Using "-machine none", the unversioned CPU models will be aliases
> > > > > to the latest CPU model version.
> > > > >
> > > > > Includes a test case to ensure that:
> > > > > old machine types won't report any alias to versioned CPU models;
> > > > > "pc-*-4.1" will return aliases to -4.1 CPU models;
> > > > > and "-machine none" will report aliases to some versioned CPU model.
> > > > >
> > > > > Signed-off-by: Eduardo Habkost <address@hidden>
> > > >
> > > > What happens when we add the next new CPU model? So say in 4.2 we add
> > > > a new CPU, does that default to being newcpu-4.2 ?
> > >
> > > We can choose between providing old versions of the CPU model
> > > retroactively ("NewModel-4.1" and "NewModel-4.2"), or providing
> > > only "NewModel-4.2".
> > >
> > > The question is: if we provide only "NewModel-4.2", what should
> > > be the behavior of "-machine pc-i440fx-4.1 -cpu NewModel"?
> >
> > Perhaps the existing CPUs and the first instance of a new CPU
> > we should use something non-numeric, e.g. 'orig' rather than 4.1;
> > we only go numeric when we cause a divergence.
>
> What would be the advantage of a non-numeric version identifier?
> I believe it would be more confusing to have (e.g.)
> ["NewModel-orig", "NewModel-4.3"] in QEMU 4.3 instead of
> ["NewModel-4.2", "NewModel-4.3"].
To my mind it answers your question:
> > > The question is: if we provide only "NewModel-4.2", what should
> > > be the behavior of "-machine pc-i440fx-4.1 -cpu NewModel"?
NewModel-orig doesn't look weird in pc-i440fx-4.1
Dave
> However, you have another interesting point: should we introduce
> -4.2 versions of all CPU models in QEMU 4.2, or only for the ones
> that actually changed? I think I prefer consistency, even if it
> means making the list of CPU models larger.
>
> What do others think?
>
> --
> Eduardo
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK
- [Qemu-devel] [PATCH 2/6] i386: Remove unused host_cpudef variable, (continued)
Re: [Qemu-devel] [PATCH 4/6] i386: Infrastructure for versioned CPU models, Daniel P . Berrangé, 2019/06/25
Re: [Qemu-devel] [PATCH 4/6] i386: Infrastructure for versioned CPU models, Daniel P . Berrangé, 2019/06/25
[Qemu-devel] [PATCH 5/6] docs: Deprecate CPU model runnability guarantees, Eduardo Habkost, 2019/06/25
[Qemu-devel] [PATCH 6/6] i386: Add Cascadelake-Server-4.1.1 CPU model, Eduardo Habkost, 2019/06/25
Re: [Qemu-devel] [PATCH 0/6] x86 CPU model versioning, no-reply, 2019/06/25