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[Qemu-devel] Re: [RFC][PATCH 0/3] Let RTC follow backward jumps of host
From: |
Jan Kiszka |
Subject: |
[Qemu-devel] Re: [RFC][PATCH 0/3] Let RTC follow backward jumps of host clock immediately |
Date: |
Wed, 26 Jan 2011 12:46:40 +0100 |
User-agent: |
Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv:1.8.1.12) Gecko/20080226 SUSE/2.0.0.12-1.1 Thunderbird/2.0.0.12 Mnenhy/0.7.5.666 |
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
--
Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux
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