From: Aritoki TAKADA <aritoki.takada.jt@hitachi.com>
To: kvm@vger.kernel.org
Cc: ltc-kernel@ml.yrl.intra.hitachi.co.jp
Subject: Question: Timekeeping between Host and Guest with NTP
Date: Wed, 22 Aug 2012 17:46:52 +0900 [thread overview]
Message-ID: <50349C7C.2070409@hitachi.com> (raw)
Hello,
I'm planning to configure timekeeping between KVM host and guest,
but I'm confused by different suggestions.
The point is whether NTP should be working on guest or not.
Here are the suggestions I found.
Red Hat document:
http://docs.redhat.com/docs/en-US/Red_Hat_Enterprise_Linux/6/html/Virtualization_Host_Configuration_and_Guest_Installation_Guide/chap-Virtualization_Host_Configuration_and_Guest_Installation_Guide-KVM_guest_timing_management.html
kvmclock : recommended if available
NTP on host : recommended
NTP on guest : recommended
Suse document:
http://doc.opensuse.org/documentation/html/openSUSE/opensuse-kvm/cha.libvirt.config.html#sec.kvm.managing.clock
kvmclock : recommended if available
NTP on host : recommended
NTP on guest : NOT recommended when using kvmclock
Ubuntu document:
https://help.ubuntu.com/community/KVM/FAQ#Should_ntp_be_used_for_time_synchronisation.3F
kvmclock : not mentioned
NTP on host : not mentioned
NTP on guest : NOT recommended
Previous discussions I found on kvm@vger.kernel.org:
Dor Laor from Red Hat says the same as the Red Hat document.
http://marc.info/?l=kvm&m=130881067913835&w=4
John Buswell and Athanasius discussed another technique,
which uses not NTP but RTC from guest to keep guest syncing to host,
but they say it isn't the best way.
http://marc.info/?l=kvm&m=127230166532133&w=4
I just tried with CentOS 6.3 as both host and guest OS,
whose kernels were replaced with 3.5.2 from upstream.
I found the guest has a little delay when booted,
which is about one or two seconds.
Without NTP on the guest, the delay seemed
constant while running.
I think NTP on the guest will fix the delay,
but I'm afraid there would be some reasons
that NTP should not be on the guest.
If you know why NTP should (not) be running on
guest, please let me know.
Thank you in advance,
--
Aritoki TAKADA
aritoki.takada.jt@hitachi.com
Hitachi, Ltd., Yokohama Research Laboratory
next reply other threads:[~2012-08-22 8:49 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-08-22 8:46 Aritoki TAKADA [this message]
2012-08-23 18:13 ` Question: Timekeeping between Host and Guest with NTP Marcelo Tosatti
2012-08-24 11:43 ` Aritoki TAKADA
2012-08-24 15:00 ` Marcelo Tosatti
2012-08-27 9:37 ` Aritoki TAKADA
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