[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.
Paolo
- Re: [Qemu-devel] [libvirt] TSC frequency configuration & invtsc migration (was Re: [PATCH 4/4] kvm: Allow migration with invtsc), (continued)
- Re: [Qemu-devel] TSC frequency configuration & invtsc migration (was Re: [PATCH 4/4] kvm: Allow migration with invtsc), Marcelo Tosatti, 2017/01/06
- [Qemu-devel] How to make dest host abort migration safely (was Re: [PATCH 4/4] kvm: Allow migration with invtsc), Eduardo Habkost, 2017/01/08
- Re: [Qemu-devel] How to make dest host abort migration safely (was Re: [PATCH 4/4] kvm: Allow migration with invtsc), Dr. David Alan Gilbert, 2017/01/09
- [Qemu-devel] Exporting kvm_max_guest_tsc_khz to userspace (was Re: [PATCH 4/4] kvm: Allow migration with invtsc), Eduardo Habkost, 2017/01/08
- Re: [Qemu-devel] Exporting kvm_max_guest_tsc_khz to userspace (was Re: [PATCH 4/4] kvm: Allow migration with invtsc), Paolo Bonzini, 2017/01/09
- Re: [Qemu-devel] Exporting kvm_max_guest_tsc_khz to userspace (was Re: [PATCH 4/4] kvm: Allow migration with invtsc), Eduardo Habkost, 2017/01/11
- Re: [Qemu-devel] Exporting kvm_max_guest_tsc_khz to userspace (was Re: [PATCH 4/4] kvm: Allow migration with invtsc),
Paolo Bonzini <=
- Re: [Qemu-devel] TSC frequency configuration & invtsc migration (was Re: [PATCH 4/4] kvm: Allow migration with invtsc), Paolo Bonzini, 2017/01/10
- Re: [Qemu-devel] TSC frequency configuration & invtsc migration (was Re: [PATCH 4/4] kvm: Allow migration with invtsc), Eduardo Habkost, 2017/01/11
- Re: [Qemu-devel] TSC frequency configuration & invtsc migration (was Re: [PATCH 4/4] kvm: Allow migration with invtsc), Marcelo Tosatti, 2017/01/18
- Re: [Qemu-devel] TSC frequency configuration & invtsc migration (was Re: [PATCH 4/4] kvm: Allow migration with invtsc), Eduardo Habkost, 2017/01/18