From: Paolo Bonzini <pbonzini@redhat.com>
To: Eduardo Habkost <ehabkost@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>,
qemu-devel@nongnu.org, kvm@vger.kernel.org,
Haozhong Zhang <haozhong.zhang@intel.com>,
libvir-list@redhat.com
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 [thread overview]
Message-ID: <fcb2f7b5-93ad-9a48-1669-936b3925c923@redhat.com> (raw)
In-Reply-To: <20170111132653.GB3315@thinpad.lan.raisama.net>
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
next prev parent reply other threads:[~2017-01-11 14:06 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-27 19:21 [Qemu-devel] [PATCH 0/4] Allow migration with invtsc if there's no frequency mismatch Eduardo Habkost
2016-12-27 19:21 ` [Qemu-devel] [PATCH 1/4] kvm: Simplify invtsc check Eduardo Habkost
2016-12-29 18:57 ` Marcelo Tosatti
2016-12-27 19:21 ` [Qemu-devel] [PATCH 2/4] kvm: Allow invtsc migration if tsc-khz is set explicitly Eduardo Habkost
2017-01-04 11:44 ` Marcelo Tosatti
2017-01-04 11:57 ` Marcelo Tosatti
2017-01-04 13:40 ` Eduardo Habkost
2017-01-04 13:45 ` Marcelo Tosatti
2017-01-04 13:51 ` Eduardo Habkost
2016-12-27 19:21 ` [Qemu-devel] [PATCH 3/4] pc: Add 2.9 machine-types Eduardo Habkost
2016-12-30 13:38 ` Igor Mammedov
2017-01-04 14:01 ` Laszlo Ersek
2017-01-04 14:20 ` Eduardo Habkost
2017-01-04 16:40 ` Laszlo Ersek
2017-01-04 17:46 ` Eduardo Habkost
2016-12-27 19:21 ` [Qemu-devel] [PATCH 4/4] kvm: Allow migration with invtsc Eduardo Habkost
2017-01-04 11:56 ` Marcelo Tosatti
2017-01-04 13:39 ` Eduardo Habkost
2017-01-04 19:59 ` [Qemu-devel] TSC frequency configuration & invtsc migration (was Re: [PATCH 4/4] kvm: Allow migration with invtsc) Eduardo Habkost
2017-01-04 22:26 ` Marcelo Tosatti
2017-01-05 1:36 ` Eduardo Habkost
2017-01-05 10:48 ` Marcelo Tosatti
2017-01-05 10:50 ` Marcelo Tosatti
2017-01-05 12:19 ` Eduardo Habkost
2017-01-05 12:33 ` [Qemu-devel] [libvirt] " Daniel P. Berrange
2017-01-05 12:48 ` Eduardo Habkost
2017-01-05 13:00 ` Daniel P. Berrange
2017-01-05 13:11 ` Eduardo Habkost
2017-01-10 16:38 ` Paolo Bonzini
2017-01-06 10:31 ` [Qemu-devel] " Marcelo Tosatti
2017-01-08 15:49 ` [Qemu-devel] How to make dest host abort migration safely " Eduardo Habkost
2017-01-09 10:04 ` Dr. David Alan Gilbert
2017-01-08 20:28 ` [Qemu-devel] Exporting kvm_max_guest_tsc_khz to userspace " Eduardo Habkost
2017-01-09 14:58 ` Paolo Bonzini
2017-01-11 13:26 ` Eduardo Habkost
2017-01-11 14:06 ` Paolo Bonzini [this message]
2017-01-10 16:36 ` [Qemu-devel] TSC frequency configuration & invtsc migration " Paolo Bonzini
2017-01-11 11:58 ` Eduardo Habkost
2017-01-18 11:55 ` Marcelo Tosatti
2017-01-18 12:43 ` Eduardo Habkost
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