From: Marcelo Tosatti <mtosatti@redhat.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>,
qemu-devel@nongnu.org, kvm@vger.kernel.org,
Haozhong Zhang <haozhong.zhang@intel.com>,
libvir-list@redhat.com
Subject: Re: [Qemu-devel] TSC frequency configuration & invtsc migration (was Re: [PATCH 4/4] kvm: Allow migration with invtsc)
Date: Wed, 18 Jan 2017 09:55:43 -0200 [thread overview]
Message-ID: <20170118115541.GA13762@amt.cnet> (raw)
In-Reply-To: <4006fc1d-f4f8-12dd-05e7-950cc839aae4@redhat.com>
On Tue, Jan 10, 2017 at 05:36:48PM +0100, Paolo Bonzini wrote:
>
>
> On 05/01/2017 11:48, Marcelo Tosatti wrote:
> >> Host A has TSC scaling, host B doesn't have TSC scaling. We want
> >> to be able to start the VM on host A, and migrate to B. In this
> >> case, the only possible solution is to use B's frequency when
> >> starting the VM. The QEMU process doesn't have enough information
> >> to make that decision.
> > That is a good point. But again, its a special case and
> > should be supported by -cpu xxx,tsc-frequency=zzzz.
>
> I don't think this is a scenario that can work reliably. The computed
> TSC frequency may vary by 0.5% or so on every boot (e.g. you may get
> 2497000 kHz or 2511000 kHz for a 2.5 GHz TSC). You can start the VM on
> host A, reboot host B, and then you'll be unable to migrate.
>
> Paolo
Including an acceptable error in the comparison seems to be acceptable to work around that
case.
next prev parent reply other threads:[~2017-01-18 12:18 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
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 [this message]
2017-01-18 12:43 ` Eduardo Habkost
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