RE: [PATCH] Drivers: hv: util: Implement Time Synchronization using host time sample

From: Thomas Shao
Date: Thu Sep 25 2014 - 05:55:45 EST

> -----Original Message-----
> From: Sitsofe Wheeler [mailto:sitsofe@xxxxxxxxx]
> Sent: Thursday, September 25, 2014 2:08 PM
> To: Olaf Hering
> Cc: Thomas Shao; gregkh@xxxxxxxxxxxxxxxxxxx; linux-
> kernel@xxxxxxxxxxxxxxx; driverdev-devel@xxxxxxxxxxxxxxxxxxxxxx;
> apw@xxxxxxxxxxxxx; jasowang@xxxxxxxxxx; KY Srinivasan; Haiyang Zhang
> Subject: Re: [PATCH] Drivers: hv: util: Implement Time Synchronization using
> host time sample
> On Tue, Sep 23, 2014 at 09:56:10AM +0200, Olaf Hering wrote:
> > On Tue, Sep 23, Thomas Shao wrote:
> >
> > > In current hyper-v time sync service,it only gets the initial clock
> > > time from the host. It didn't process the following time samples.
> > > This change introduced a module parameter called host_time_sync. If
> > > it is set to true, the guest will periodically sychronize it's time
> > > with the host clock using host time sample. By default it is
> > > disabled, because we still recommend user to configure NTP for time
> synchronization.
> You [Microsoft?] do? Can you link to public sources where is this stated
> please? I don't see any mention of doing this on
> .. The only
> official Microsoft information with respect to Hyper-V guest time
> synchronisation I've seen has been for Windows guests but perhaps I've
> looked in the wrong places.
> The reason I ask is because regular ntpd is not enough to discipline a Linux
> Hyper-V guest's clock. So much drift can occur under load that ntpd can't
> bring the clock under sync. For now, I've been using Chrony which has a
> higher tolerance for correcting drifting clocks. I'm not the only one seeing this
> either (see
> and
> every-week
> ).
> It would be good to something official about this issue as it is painful when
> happens.

Hi Sitsofe,

As far as I know, currently the document about time sync in Hyper-V is only for Windows. Below is a doc from MSDN:
We are working on the document about Time Sync on Hyper-V to cover both Linux and Windows.

> --
> Sitsofe |
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