From: Dor Laor <dlaor@redhat.com>
To: Chaitra Gorantla <Chaitra.Gorantla@lntinfotech.com>
Cc: KVM devel mailing list <kvm@vger.kernel.org>
Subject: Re: Time sync in KVM Guest
Date: Wed, 22 Jun 2011 11:19:28 +0300 [thread overview]
Message-ID: <4E01A590.60906@redhat.com> (raw)
In-Reply-To: <AF0985D076EB244693F2CCD71AAB10BC0CD17EF30A@BLRINMSMBX01.bglrodc.lntinfotech.com>
On 06/22/2011 06:17 AM, Chaitra Gorantla wrote:
> Hi all,
>
> We are working on Fedora 15 Host. And the KVM is used to create Fedora 14 guest.
> The clock-source details are as below.
>
> Our Host supports constant_tsc.
>
> on HOST OS
> cat /sys/devices/system/clocksource/clocksource0/current_clocksource
> tsc
>
> on GUEST OS
> cat /sys/devices/system/clocksource/clocksource0/current_clocksource
> kvm-clock
>
> We are not having Wall-clock time Sync in Both Host and guest.
> The Time in Host OS lags behind guest by atleast 2 seconds.
> However, this time difference remains constant.
That's good
> Does this mean that the Host and Guest clocks are synchronized ?
> By using kvm-clock as clock source on the guest, the time sync should happen itself ?
> Please correct me if I am wrong...
> How exactly we can find the time difference between Host and guest?
Usually Linux OS reads the rtc cmos to get the time when it boots.
Both the guest and the host do that using hwclock.
From there own the time is tracked by the clock source as delta.
It is recommended that both the guest and the host will run ntpd to keep
their time updated. That's the only thing that you're recommended to do.
Thanks,
dor
>
> Thanks in advance.
>
>
>
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next prev parent reply other threads:[~2011-06-22 8:19 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-06-22 3:17 Time sync in KVM Guest Chaitra Gorantla
2011-06-22 8:19 ` Dor Laor [this message]
2011-06-23 6:31 ` Chaitra Gorantla
2011-06-23 9:22 ` Dor Laor
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