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Re: [Qemu-devel] time synchronization with qemu
From: |
Piotr Krysik |
Subject: |
Re: [Qemu-devel] time synchronization with qemu |
Date: |
Wed, 15 Sep 2004 07:37:11 -0700 (PDT) |
Hi!
When qemu is waiting to read data from your host
disk, the clock may slow down. For start try to
work on small images that fit in ram.
My guess is that your guest uses timer interrupt
as time source and when there should be two or more
interrupts while qemu is waiting for disk read
to complete, only first interrupt will be delivered.
The solution is to modify qemu source code to use
asynchronous disk IO. A patch was send on this list
a few months ago (search the list archive for AIO),
but I didn't try (or even analyze it), so I cannot
tell if it can help.
Regards,
Piotrek
--- giovanni bracco <address@hidden> wrote:
> I have tried but it does not works well and I
> think that the reason is that inside a qemu system
> the clock is not stable and depends on the load
> of the ost machine (which depends, in my case of
> the 3 qemu running together, also on the load on
> the other qemu systems). I suppose that ntp does
> not work well with very unstable clocks!
>
> Up to now the best solution I have found is to
> run a cron job on the host which sets every minute
> the clock of the 3 qemu systems using "rsh rdate
> -s host.ip" but still the time difference between
> qemu systems is til between 3 and 10 seconds (even
> if there is a reset about every minute!)
>
> Any suggestion is welll accepted!
>
> Giovanni
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