Is ntpd in guest necessary?

Is ntpd in guest necessary?

[Michael Tokarev]

A question that I asked on irc many times,
but got no answer..

Giving guest linux with CONFIG_KVM_TIME set,
is it necessary to run ntpd in it for accurate
time, or ntpd on host is sufficient?

And the same, but without CONFIG_KVM_TIME ?

Thanks!

/mjt

Re: Is ntpd in guest necessary?

[David Mair]

Michael Tokarev wrote:
> A question that I asked on irc many times,
> but got no answer..
>
> Giving guest linux with CONFIG_KVM_TIME set,
> is it necessary to run ntpd in it for accurate
> time, or ntpd on host is sufficient?
>
> And the same, but without CONFIG_KVM_TIME ?

What was your experience when you tested with each config?

-- 
David.

Re: Is ntpd in guest necessary?

[Avi Kivity]

Michael Tokarev wrote:
> A question that I asked on irc many times,
> but got no answer..
>
> Giving guest linux with CONFIG_KVM_TIME set,
> is it necessary to run ntpd in it for accurate
> time, or ntpd on host is sufficient?
>
> And the same, but without CONFIG_KVM_TIME ?
>   

In theory, CONFIG_KVM_CLOCK should avoid the need for ntp.  Let us know 
if you get different results.

-- 
error compiling committee.c: too many arguments to function

Re: Is ntpd in guest necessary?

[Alberto Treviño]

On Sunday 16 November 2008 07:27:48 am you wrote:
> In theory, CONFIG_KVM_CLOCK should avoid the need for ntp.  Let us know
> if you get different results.

I've been running a VM for a couple of days with a 2.6.27 kernel and 
CONFIG_KVM_CLOCK and the clock is synchronized.  Is there a driver we could 
use on Windows to keep the clock synchronized there as well?

Re: Is ntpd in guest necessary?

[Michael Tokarev]

Avi Kivity wrote:
> Michael Tokarev wrote:
>> A question that I asked on irc many times,
>> but got no answer..
>>
>> Giving guest linux with CONFIG_KVM_TIME set,
>> is it necessary to run ntpd in it for accurate
>> time, or ntpd on host is sufficient?
>>
>> And the same, but without CONFIG_KVM_TIME ?
> 
> In theory, CONFIG_KVM_CLOCK should avoid the need for ntp.  Let us know 
> if you get different results.

Well.  The question was not come from nowhere.
It *seems* like it is working, but somewhat.. strange.
I.e., when the time steps on the host (for whatever reason),
it stays the same on guests, at least for some time.  Later
on it syncronizes, *sometimes*, but not always.  I tried to
reproduce this unsyncronization (hence the delay with replying),
but can't do it easily "on demand".  Maybe I were just dreaming
at the time I saw it, but I don't think so.  Or maybe something
has changed in recent kernels/kvm so that it does not happen
any more.  That's why I asked in the first place.

In short: with CONFIG_KVM_TIME set, it *seems* to work, but
I'm not 100% sure still.  The question was if it *supposed*
to work in the first place, and you answered that.

And withOUT CONFIG_KVM_TIME, it stays unsyncronized.

Thanks!

/mjt