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Re: [Qemu-devel] [patch 2/2] target-i386: block migration and savevm if
From: |
Eduardo Habkost |
Subject: |
Re: [Qemu-devel] [patch 2/2] target-i386: block migration and savevm if invariant tsc is exposed |
Date: |
Mon, 28 Apr 2014 16:23:37 -0300 |
User-agent: |
Mutt/1.5.21 (2010-09-15) |
On Mon, Apr 28, 2014 at 09:06:42PM +0200, Paolo Bonzini wrote:
> Il 28/04/2014 17:46, Eduardo Habkost ha scritto:
> >>So I couldn't indeed think of uses of "-cpu host" together with
> >>migration. But if you're sure there is none, block it in QEMU.
> >>There's no reason why this should be specific to libvirt.
> >
> >It's not that there are no useful use cases, it is that we simply can't
> >guarantee it will work because (by design) "-cpu host" enables features
> >QEMU doesn't know about (so it doesn't know if migration is safe or
> >not). And that's the main use case for "-cpu host".
>
> True, but in practice QEMU and KVM support is added in parallel, and
> we already have full support for Broadwell (IIRC) and are starting to
> add Skylake features.
>
> >So, what about doing the following on QEMU 2.1:
> >
> > * "-cpu host,migratable=yes":
> > * No invtsc
> > * Migration not blocked
> > * No feature flag unknown to QEMU will be enabled
> > * "-cpu host,migratable=no":
> > * invtsc enabled
> > * Unknown-to-QEMU features enabled
> > * Migration blocked
> > * "-cpu host":
> > * Same behavior as "-cpu host,migratable=yes"
> > * Release notes indicating that "-cpu host,migratable=no" is
> > required if the user doesn't care about migration and wants new
> > (unknown to QEMU) features to be available
> >
> >I was going to propose making "migratable=no" the default after a few
> >releases, as I expect the majority of existing users of "-cpu host" to
> >not care about migration. But I am not sure, because there's less harm
> >in _not_ getting new bleeding edge features enabled, and those users
> >(and management software) can start using "migratable=no" if they really
> >want the new unmigratable features.
>
> Makes sense. Basically "-cpu host,migratable=yes" is close to
> libvirt's host-model and Alex Graf's proposed "-cpu best". Should we
> call it "-cpu best" and drop migratability of "-cpu host"?
"-cpu best" is different from the modes above. It means "use the best
existing CPU model (from the pre-defined table) that can run on this
host".
And it would have the same ambiguities we found on "-cpu host": if a CPU
model in the table have invtsc enabled, should it be considered a
candidate for "-cpu best", or not?
--
Eduardo
- Re: [Qemu-devel] [patch 2/2] target-i386: block migration and savevm if invariant tsc is exposed, (continued)
- Re: [Qemu-devel] [patch 2/2] target-i386: block migration and savevm if invariant tsc is exposed, Eduardo Habkost, 2014/04/22
- Re: [Qemu-devel] [patch 2/2] target-i386: block migration and savevm if invariant tsc is exposed, Marcelo Tosatti, 2014/04/22
- Re: [Qemu-devel] [patch 2/2] target-i386: block migration and savevm if invariant tsc is exposed, Eduardo Habkost, 2014/04/22
- Re: [Qemu-devel] [patch 2/2] target-i386: block migration and savevm if invariant tsc is exposed, Paolo Bonzini, 2014/04/24
- Re: [Qemu-devel] [patch 2/2] target-i386: block migration and savevm if invariant tsc is exposed, Eduardo Habkost, 2014/04/24
- Re: [Qemu-devel] [patch 2/2] target-i386: block migration and savevm if invariant tsc is exposed, Paolo Bonzini, 2014/04/24
- Re: [Qemu-devel] [patch 2/2] target-i386: block migration and savevm if invariant tsc is exposed, Eduardo Habkost, 2014/04/24
- Re: [Qemu-devel] [patch 2/2] target-i386: block migration and savevm if invariant tsc is exposed, Paolo Bonzini, 2014/04/25
- Re: [Qemu-devel] [patch 2/2] target-i386: block migration and savevm if invariant tsc is exposed, Eduardo Habkost, 2014/04/28
- Re: [Qemu-devel] [patch 2/2] target-i386: block migration and savevm if invariant tsc is exposed, Paolo Bonzini, 2014/04/28
- Re: [Qemu-devel] [patch 2/2] target-i386: block migration and savevm if invariant tsc is exposed,
Eduardo Habkost <=
- Re: [Qemu-devel] [patch 2/2] target-i386: block migration and savevm if invariant tsc is exposed, Paolo Bonzini, 2014/04/29
- Re: [Qemu-devel] [patch 2/2] target-i386: block migration and savevm if invariant tsc is exposed, Eduardo Habkost, 2014/04/29
[Qemu-devel] [patch 1/2] target-i386: support "invariant tsc" flag, Marcelo Tosatti, 2014/04/22
[Qemu-devel] [patch 0/2] expose invariant tsc flag for kvm guests (v2), Marcelo Tosatti, 2014/04/23