From: Paolo Bonzini <pbonzini@redhat.com>
To: "Daniel P. Berrange" <berrange@redhat.com>,
Eduardo Habkost <ehabkost@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>,
libvir-list@redhat.com, qemu-devel@nongnu.org,
kvm@vger.kernel.org, Haozhong Zhang <haozhong.zhang@intel.com>
Subject: Re: [libvirt] TSC frequency configuration & invtsc migration (was Re: [PATCH 4/4] kvm: Allow migration with invtsc)
Date: Tue, 10 Jan 2017 17:38:45 +0100 [thread overview]
Message-ID: <1ec51249-59c8-582b-d3cb-3389606649ce@redhat.com> (raw)
In-Reply-To: <20170105130032.GJ3292@redhat.com>
On 05/01/2017 14:00, Daniel P. Berrange wrote:
>> If you do this unconditionally, you have another problem: if
>> tsc-frequency is set explicitly, migration is only possible if
>> TSC frequency of the destination matches[1], or if TSC scaling is
>> supported by the destination. It's a good idea to set a TSC
>> frequency only if invtsc is enabled explicitly in the config.
>
> If we don't set tsc-frequency and the TSC frequency doesn't
> match, does that mean the guest migration succeed, but suddenly
> sees different TSC frequency ?
That's the reason why kvmclock exists (or more precisely, the reason why
kvmclock is still useful even when hosts have invtsc).
Paolo
> I guess we we allowed that historically we can't break that
> now, so setting it only if invtsc is set seems reasonable.
WARNING: multiple messages have this Message-ID (diff)
From: Paolo Bonzini <pbonzini@redhat.com>
To: "Daniel P. Berrange" <berrange@redhat.com>,
Eduardo Habkost <ehabkost@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>,
libvir-list@redhat.com, qemu-devel@nongnu.org,
kvm@vger.kernel.org, Haozhong Zhang <haozhong.zhang@intel.com>
Subject: Re: [Qemu-devel] [libvirt] TSC frequency configuration & invtsc migration (was Re: [PATCH 4/4] kvm: Allow migration with invtsc)
Date: Tue, 10 Jan 2017 17:38:45 +0100 [thread overview]
Message-ID: <1ec51249-59c8-582b-d3cb-3389606649ce@redhat.com> (raw)
In-Reply-To: <20170105130032.GJ3292@redhat.com>
On 05/01/2017 14:00, Daniel P. Berrange wrote:
>> If you do this unconditionally, you have another problem: if
>> tsc-frequency is set explicitly, migration is only possible if
>> TSC frequency of the destination matches[1], or if TSC scaling is
>> supported by the destination. It's a good idea to set a TSC
>> frequency only if invtsc is enabled explicitly in the config.
>
> If we don't set tsc-frequency and the TSC frequency doesn't
> match, does that mean the guest migration succeed, but suddenly
> sees different TSC frequency ?
That's the reason why kvmclock exists (or more precisely, the reason why
kvmclock is still useful even when hosts have invtsc).
Paolo
> I guess we we allowed that historically we can't break that
> now, so setting it only if invtsc is set seems reasonable.
next prev parent reply other threads:[~2017-01-10 16:38 UTC|newest]
Thread overview: 78+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-12-27 19:21 [PATCH 0/4] Allow migration with invtsc if there's no frequency mismatch Eduardo Habkost
2016-12-27 19:21 ` [Qemu-devel] " Eduardo Habkost
2016-12-27 19:21 ` [PATCH 1/4] kvm: Simplify invtsc check Eduardo Habkost
2016-12-27 19:21 ` [Qemu-devel] " Eduardo Habkost
2016-12-29 18:57 ` Marcelo Tosatti
2016-12-29 18:57 ` [Qemu-devel] " Marcelo Tosatti
2016-12-27 19:21 ` [PATCH 2/4] kvm: Allow invtsc migration if tsc-khz is set explicitly Eduardo Habkost
2016-12-27 19:21 ` [Qemu-devel] " Eduardo Habkost
2017-01-04 11:44 ` Marcelo Tosatti
2017-01-04 11:44 ` [Qemu-devel] " Marcelo Tosatti
2017-01-04 11:57 ` Marcelo Tosatti
2017-01-04 11:57 ` [Qemu-devel] " Marcelo Tosatti
2017-01-04 13:40 ` Eduardo Habkost
2017-01-04 13:40 ` [Qemu-devel] " Eduardo Habkost
2017-01-04 13:45 ` Marcelo Tosatti
2017-01-04 13:45 ` [Qemu-devel] " Marcelo Tosatti
2017-01-04 13:51 ` Eduardo Habkost
2017-01-04 13:51 ` [Qemu-devel] " Eduardo Habkost
2016-12-27 19:21 ` [PATCH 3/4] pc: Add 2.9 machine-types Eduardo Habkost
2016-12-27 19:21 ` [Qemu-devel] " Eduardo Habkost
2016-12-30 13:38 ` Igor Mammedov
2016-12-30 13:38 ` [Qemu-devel] " Igor Mammedov
2017-01-04 14:01 ` Laszlo Ersek
2017-01-04 14:20 ` Eduardo Habkost
2017-01-04 14:20 ` [Qemu-devel] " Eduardo Habkost
2017-01-04 16:40 ` Laszlo Ersek
2017-01-04 16:40 ` [Qemu-devel] " Laszlo Ersek
2017-01-04 17:46 ` Eduardo Habkost
2016-12-27 19:21 ` [PATCH 4/4] kvm: Allow migration with invtsc Eduardo Habkost
2016-12-27 19:21 ` [Qemu-devel] " Eduardo Habkost
2017-01-04 11:56 ` Marcelo Tosatti
2017-01-04 11:56 ` [Qemu-devel] " Marcelo Tosatti
2017-01-04 13:39 ` Eduardo Habkost
2017-01-04 13:39 ` [Qemu-devel] " Eduardo Habkost
2017-01-04 19:59 ` [libvirt] TSC frequency configuration & invtsc migration (was Re: [PATCH 4/4] kvm: Allow migration with invtsc) Eduardo Habkost
2017-01-04 19:59 ` [Qemu-devel] " Eduardo Habkost
2017-01-04 22:26 ` Marcelo Tosatti
2017-01-04 22:26 ` [Qemu-devel] " Marcelo Tosatti
2017-01-05 1:36 ` Eduardo Habkost
2017-01-05 1:36 ` [Qemu-devel] " Eduardo Habkost
2017-01-05 10:48 ` Marcelo Tosatti
2017-01-05 10:48 ` [Qemu-devel] " Marcelo Tosatti
2017-01-05 10:50 ` Marcelo Tosatti
2017-01-05 10:50 ` [Qemu-devel] " Marcelo Tosatti
2017-01-05 12:19 ` Eduardo Habkost
2017-01-05 12:19 ` [Qemu-devel] " Eduardo Habkost
2017-01-05 12:33 ` [libvirt] " Daniel P. Berrange
2017-01-05 12:33 ` [Qemu-devel] " Daniel P. Berrange
2017-01-05 12:48 ` Eduardo Habkost
2017-01-05 12:48 ` [Qemu-devel] " Eduardo Habkost
2017-01-05 13:00 ` Daniel P. Berrange
2017-01-05 13:00 ` [Qemu-devel] " Daniel P. Berrange
2017-01-05 13:11 ` Eduardo Habkost
2017-01-05 13:11 ` [Qemu-devel] " Eduardo Habkost
2017-01-10 16:38 ` Paolo Bonzini [this message]
2017-01-10 16:38 ` Paolo Bonzini
2017-01-06 10:31 ` Marcelo Tosatti
2017-01-06 10:31 ` [Qemu-devel] " Marcelo Tosatti
2017-01-08 15:49 ` How to make dest host abort migration safely " Eduardo Habkost
2017-01-08 15:49 ` [Qemu-devel] " Eduardo Habkost
2017-01-09 10:04 ` [libvirt] " Dr. David Alan Gilbert
2017-01-09 10:04 ` [Qemu-devel] " Dr. David Alan Gilbert
2017-01-08 20:28 ` Exporting kvm_max_guest_tsc_khz to userspace " Eduardo Habkost
2017-01-08 20:28 ` [Qemu-devel] " Eduardo Habkost
2017-01-09 14:58 ` Paolo Bonzini
2017-01-09 14:58 ` [Qemu-devel] " Paolo Bonzini
2017-01-11 13:26 ` Eduardo Habkost
2017-01-11 13:26 ` [Qemu-devel] " Eduardo Habkost
2017-01-11 14:06 ` Paolo Bonzini
2017-01-11 14:06 ` [Qemu-devel] " Paolo Bonzini
2017-01-10 16:36 ` TSC frequency configuration & invtsc migration " Paolo Bonzini
2017-01-10 16:36 ` [Qemu-devel] " Paolo Bonzini
2017-01-11 11:58 ` Eduardo Habkost
2017-01-11 11:58 ` [Qemu-devel] " Eduardo Habkost
2017-01-18 11:55 ` Marcelo Tosatti
2017-01-18 11:55 ` [Qemu-devel] " Marcelo Tosatti
2017-01-18 12:43 ` Eduardo Habkost
2017-01-18 12:43 ` [Qemu-devel] " Eduardo Habkost
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