From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
To: Eduardo Habkost <ehabkost@redhat.com>
Cc: "Daniel P. Berrange" <berrange@redhat.com>,
qemu-devel@nongnu.org, Paolo Bonzini <pbonzini@redhat.com>,
Igor Mammedov <imammedo@redhat.com>,
Jiri Denemark <jdenemar@redhat.com>,
Richard Henderson <rth@twiddle.net>
Subject: Re: [Qemu-devel] [PATCH 4/6] i386: Infrastructure for versioned CPU models
Date: Tue, 25 Jun 2019 15:56:51 +0100 [thread overview]
Message-ID: <20190625145651.GM3226@work-vm> (raw)
In-Reply-To: <20190625145309.GQ1862@habkost.net>
* Eduardo Habkost (ehabkost@redhat.com) wrote:
> On Tue, Jun 25, 2019 at 03:32:16PM +0100, Dr. David Alan Gilbert wrote:
> > * Eduardo Habkost (ehabkost@redhat.com) wrote:
> > > On Tue, Jun 25, 2019 at 10:32:01AM +0100, Dr. David Alan Gilbert wrote:
> > > > * Eduardo Habkost (ehabkost@redhat.com) 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 <ehabkost@redhat.com>
> > > >
> > > > 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 / dgilbert@redhat.com / Manchester, UK
next prev parent reply other threads:[~2019-06-25 15:05 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-25 5:00 [Qemu-devel] [PATCH 0/6] x86 CPU model versioning Eduardo Habkost
2019-06-25 5:00 ` [Qemu-devel] [PATCH 1/6] i386: Add x-force-features option for testing Eduardo Habkost
2019-06-25 5:00 ` [Qemu-devel] [PATCH 2/6] i386: Remove unused host_cpudef variable Eduardo Habkost
2019-06-25 9:04 ` Dr. David Alan Gilbert
2019-06-25 5:00 ` [Qemu-devel] [PATCH 3/6] qmp: Add "alias-of" field to query-cpu-definitions Eduardo Habkost
2019-06-25 16:15 ` Daniel P. Berrangé
2019-06-25 18:00 ` Eduardo Habkost
2019-06-25 5:00 ` [Qemu-devel] [PATCH 4/6] i386: Infrastructure for versioned CPU models Eduardo Habkost
2019-06-25 9:32 ` Dr. David Alan Gilbert
2019-06-25 13:40 ` Eduardo Habkost
2019-06-25 14:32 ` Dr. David Alan Gilbert
2019-06-25 14:53 ` Eduardo Habkost
2019-06-25 14:56 ` Dr. David Alan Gilbert [this message]
2019-06-25 16:05 ` Eduardo Habkost
2019-06-25 16:26 ` Daniel P. Berrangé
2019-06-25 17:59 ` Eduardo Habkost
2019-06-25 18:08 ` Daniel P. Berrangé
2019-06-25 18:11 ` Eduardo Habkost
2019-06-25 5:00 ` [Qemu-devel] [PATCH 5/6] docs: Deprecate CPU model runnability guarantees Eduardo Habkost
2019-06-25 5:00 ` [Qemu-devel] [PATCH 6/6] i386: Add Cascadelake-Server-4.1.1 CPU model Eduardo Habkost
2019-06-25 5:35 ` Tao Xu
2019-06-25 13:11 ` Eduardo Habkost
2019-06-25 5:15 ` [Qemu-devel] [PATCH 0/6] x86 CPU model versioning no-reply
2019-06-25 16:13 ` Daniel P. Berrangé
2019-06-25 18:11 ` Eduardo Habkost
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