Re: Question: Timekeeping between Host and Guest with NTP

[Aritoki TAKADA <aritoki.takada.jt@hitachi.com>]

Hello,

(2012/08/25 0:00), Marcelo Tosatti wrote:
<snip>

> kvmclock driver has access to the ntpd corrected frequency of the host, but:
>
> 1) kvmclock time as reported to the guest uses the TSC as an offset in
> addition to the host monotonic clock, TSC is susceptible to frequency
> variations.
>
> The guest has its own timekeeping (it accumulates time from kvmclock,
> at every timer interrupt). The algorithm is not
> perfect, and its suspectible to small variations.
>
> These add up over time.
>
> 2) Corrections to UTC, such as leap seconds, are not reflected to the
> host monotonic clock. NTP algorithm in the guest is responsible for
> synchronization to UTC.

I see, I understood the pitfalls of the guest only syncing to kvmclock,
and now NTP on the guest seems simple and reasonable for me.
Thank you again for your detailed explanation.

Sincerely,

---
Aritoki TAKADA
aritoki.takada.jt@hitachi.com
Hitachi, Ltd., Yokohama Research Laboratory