[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Qemu-devel] Exporting kvm_max_guest_tsc_khz to userspace (was Re: [

From: Paolo Bonzini
Subject: Re: [Qemu-devel] Exporting kvm_max_guest_tsc_khz to userspace (was Re: [PATCH 4/4] kvm: Allow migration with invtsc)
Date: Wed, 11 Jan 2017 15:06:07 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.5.1

On 11/01/2017 14:26, Eduardo Habkost wrote:
> On Mon, Jan 09, 2017 at 03:58:11PM +0100, Paolo Bonzini wrote:
>> On 08/01/2017 21:28, Eduardo Habkost wrote:
>>>> Well just export KVM_GET_TSC_KHZ in a QMP command right? Its pretty
>>>> easy.
>>>> Let me know if you need any help coding or testing.
>>> I just found out that KVM doesn't provide something that QEMU and
>>> libvirt need: the value of kvm_max_guest_tsc_khz. Without it, we
>>> have no way to know if a given VM is really migratable to a host.
>>> Could we add a KVM_CAP_MAX_TSC_KHZ capability for that?
>> The ratio is really quite high, 256x the host frequency for AMD and
>> 65536x for Intel.  Anything below 2^32 Hz (above that, there would
>> probably be other failures) is safe.
> 2^32 Hz (~4.3 GHz) sounds like a limit likely to be hit by future
> CPUs. Which kind of failures do you think we could see?

Just integer overflows.  Current CPUs have been at 3.9 GHz for a while now.


reply via email to

[Prev in Thread] Current Thread [Next in Thread]