From: Thomas Shao <huishao@microsoft.com>
To: Richard Cochran <richardcochran@gmail.com>
CC: "tglx@linutronix.de" <tglx@linutronix.de>,
        "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "devel@linuxdriverproject.org" <devel@linuxdriverproject.org>,
        "olaf@aepfle.de" <olaf@aepfle.de>,
        "apw@canonical.com" <apw@canonical.com>,
        "jasowang@redhat.com" <jasowang@redhat.com>,
        KY Srinivasan <kys@microsoft.com>
Subject: RE: [PATCH 2/2] hyperv: Implement Time Synchronization using host
 time sample
Thread-Topic: [PATCH 2/2] hyperv: Implement Time Synchronization using host
 time sample
Thread-Index: AQHP55ZRTp/VO8CmfEuTJogFjyVUzJwve/cAgAAPyNCAAAnTgIAAC9dA
Date: Tue, 14 Oct 2014 14:12:02 +0000
Message-ID: <CD2CABCB2C0A0D4682C5F8AD840141540BFF21@HKXPRD3002MB006.064d.mgd.msft.net>
References: <1413285078-7027-1-git-send-email-huishao@microsoft.com>
 <20141014115412.GC4019@localhost.localdomain>
 <CD2CABCB2C0A0D4682C5F8AD840141540BFD41@HKXPRD3002MB006.064d.mgd.msft.net>
 <20141014132551.GB5994@localhost.localdomain>
In-Reply-To: <20141014132551.GB5994@localhost.localdomain>
Accept-Language: en-US
Content-Language: en-US
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 8BIT
MIME-Version: 1.0
Sender: linux-kernel-owner@vger.kernel.org


> -----Original Message-----
> From: Richard Cochran [mailto:richardcochran@gmail.com]
> Sent: Tuesday, October 14, 2014 9:26 PM
> To: Thomas Shao
> Cc: tglx@linutronix.de; gregkh@linuxfoundation.org; linux-
> kernel@vger.kernel.org; devel@linuxdriverproject.org; olaf@aepfle.de;
> apw@canonical.com; jasowang@redhat.com; KY Srinivasan
> Subject: Re: [PATCH 2/2] hyperv: Implement Time Synchronization using host
> time sample
> 
> On Tue, Oct 14, 2014 at 01:04:35PM +0000, Thomas Shao wrote:
> > > I really don't see the need for this. We have NTP. If the guests
> > > want to, they may use it. Otherwise, they have a free running clock, just
> like real machines.
> > >
> > Sometimes the user can't setup NTP. For example the guest OS didn't
> > have network connection. And in some cases, they may want the guest
> time sync with host.
> > With the existing hyper-v time source, the system clock will has
> > around 1.5 second time drift per day. If the workload in the host is heavy,
> the number could be larger.
> > So this feature is really useful for some scenarios.
> 
> Any real machine without networking (and without GPS etc) will drift. That is
> just life, tough as it is. Why should we treat these guests any differently than
> real machines?
> 
> Furthermore, without networking you really don't have a compelling need
> for correct absolute time in the first place.

The host machine can be configure with NTP. And in this case, making guest time sync
with host is useful. 

> 
> Thanks,
> Richard
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/