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Re: [Qemu-devel] [PATCH] re-set rtc date on reset handler


From: Dor Laor
Subject: Re: [Qemu-devel] [PATCH] re-set rtc date on reset handler
Date: Tue, 08 Sep 2009 17:55:28 +0300
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On 09/02/2009 02:00 AM, Glauber Costa wrote:
On Tue, Sep 1, 2009 at 1:56 PM, Blue Swirl<address@hidden>  wrote:
On Tue, Sep 1, 2009 at 7:22 PM, Glauber Costa<address@hidden>  wrote:
guests without a stable timesource such as kvm-clock will grab the wallclock
from our rtc chip. However, we only sync the date when we first launch qemu.
If a guest goes through a series of reboot cycles, it will slowly see time
getting far behind the host.

The proposal of this patch is to set the date to host clock again in the reset
handler. With this patch, I see a Fedora guest keeping its clock in sync upon
an ulimited number of reboots.

A different approach is used in m48t59.c: the guest clock is generated
directly from host clock without any timers and only a fixed offset
You mean at every ioport read? I actually thought about that, but was
too lazy...



You also need to handle the -startdate flag of qemu.
In this case you need to keep the offset and not read the host time.




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