From: "Radim Krčmář" <rkrcmar@redhat.com>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Peter Hornyack <peterhornyack@google.com>,
Marcelo Tosatti <mtosatti@redhat.com>,
Owen Hofmann <osh@google.com>, KVM General <kvm@vger.kernel.org>,
Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: What time is it kvm-clock?
Date: Thu, 25 Feb 2016 12:13:29 +0100 [thread overview]
Message-ID: <20160225111328.GA18319@potion.redhat.com> (raw)
In-Reply-To: <20160224205323.GB6355@potion.redhat.com>
2016-02-24 21:53+0100, Radim Krčmář:
> 2016-02-24 12:24-0800, Andy Lutomirski:
>> On Wed, Feb 24, 2016 at 12:17 PM, Radim Krčmář <rkrcmar@redhat.com> wrote:
>>> Do you find anything incorrect with
>>> * kvmclock measures the flow of time.
>>> * time in kvmclock flows at the same rate as host's CLOCK_BOOTTIME.
>>> ?
>>
>> If we could supply CLOCK_REALTIME as well and advertise that fact to
>> guest userspace (perhaps with a sysctl or similar in the guest to turn
>> it on), it would be *awesome*. Guests with access to this feature
>> could simply not run ntpd/chronyd.
>
> I think that pvclock_wall_clock interface is there to do that.
> (If pvclock_vcpu_time_info can provide what is claimed above.)
>
> If pvclock_wall_clock version field matches with pvclock_vcpu_time_info,
Correction: versioning schemes are independent. (pvclock_wall_clock
needs a version because of CPUs that can't atomically access 64 bits.)
> then the guest can add those two and get CLOCK_REALTIME.
pvclock_wall_clock provides CLOCK_REALTIME when pvclock_wall_clock was
0, so the guest can just add them to get current CLOCK_REALTIME.
(The agreement is that CLOCK_REALTIME started in 1970.)
next prev parent reply other threads:[~2016-02-25 11:13 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-24 2:31 What time is it kvm-clock? Owen Hofmann
2016-02-24 3:57 ` Marcelo Tosatti
2016-02-24 17:35 ` Peter Hornyack
2016-02-24 20:17 ` Radim Krčmář
2016-02-24 20:24 ` Andy Lutomirski
2016-02-24 20:53 ` Radim Krčmář
2016-02-25 11:13 ` Radim Krčmář [this message]
2016-02-25 11:22 ` Marcelo Tosatti
2016-02-24 23:35 ` Marcelo Tosatti
2016-02-24 23:36 ` Marcelo Tosatti
2016-02-25 1:19 ` Andy Lutomirski
2016-02-25 3:50 ` Owen Hofmann
2016-02-25 12:20 ` Radim Krčmář
2016-02-26 17:02 ` Andy Lutomirski
2016-02-26 19:30 ` Marcelo Tosatti
2016-02-27 0:00 ` Andy Lutomirski
2016-02-25 11:36 ` Radim Krčmář
2016-02-25 12:12 ` Marcelo Tosatti
2016-02-24 3:59 ` Marcelo Tosatti
2016-02-24 14:14 ` Paolo Bonzini
2016-02-24 16:44 ` Andy Lutomirski
2016-02-24 17:38 ` Marcelo Tosatti
2016-02-24 19:38 ` Andy Lutomirski
2016-02-24 19:44 ` Paolo Bonzini
2016-02-24 19:52 ` Andy Lutomirski
2016-02-24 19:55 ` Owen Hofmann
2016-02-25 12:22 ` Joao Martins
2016-02-25 12:22 ` Joao Martins
2016-02-26 15:04 ` Marcelo Tosatti
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