[Qemu-devel] Re: [RFC][PATCH 0/3] Let RTC follow backward jumps of host clock immediately

[Jan Kiszka <jan.kiszka@siemens.com>]

On 2010-12-17 15:58, Jan Kiszka wrote:
> By default, we base the mc146818 RTC on the host clock (CLOCK_REALTIME).
> This works fine if only the frequency of the host clock is tuned (e.g.
> by NTP) or if it is set to a future time. However, if the host is tuned
> backward, e.g. because NTP obtained the correct time after the guest was
> already started or the admin decided to tune the local time, we see an
> unpleasant effect in the guest: The RTC will stall for the period the
> host clock is set back.
> 
> This series tries to address the issue more gracefully. By detecting
> those warps and providing a callback mechanism to device models, the
> RTC is enabled to update its timers and register content immediately.
> Tested successfully with a hwclock readout loop in a Linux guest while
> fiddling with the host time.
> 
> Note that if this kind of RTC adjustment is not wanted, the user is
> still free to decouple the RTC from the host clock and base it on the
> VM clock - just like before.
> 
> Jan Kiszka (3):
>   qemu-timer: Consolidate qemu_get_clock and qemu_get_clock_ns
>   qemu-timer: Introduce warp callback
>   mc146818rtc: Handle host clock warps
> 
>  hw/mc146818rtc.c |   17 ++++++++++++
>  qemu-timer.c     |   77 ++++++++++++++++++++++++++++++++++++++++++++----------
>  qemu-timer.h     |    5 +++
>  3 files changed, 85 insertions(+), 14 deletions(-)
> 

Ping?

Jan

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