* kvm live migration reliable?
@ 2009-07-31 2:52 Kent Tong
2009-07-31 4:13 ` Stephane Bakhos
2009-07-31 13:11 ` Anthony Liguori
0 siblings, 2 replies; 3+ messages in thread
From: Kent Tong @ 2009-07-31 2:52 UTC (permalink / raw)
To: kvm
Hi,
I was wondering the kvm live migration function is reliable? I read that if
the TSC is not monotonically increasing, then the guest will hang. How to
prevent this?
Thanks!
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: kvm live migration reliable?
2009-07-31 2:52 kvm live migration reliable? Kent Tong
@ 2009-07-31 4:13 ` Stephane Bakhos
2009-07-31 13:11 ` Anthony Liguori
1 sibling, 0 replies; 3+ messages in thread
From: Stephane Bakhos @ 2009-07-31 4:13 UTC (permalink / raw)
To: Kent Tong; +Cc: kvm
> I was wondering the kvm live migration function is reliable? I read that if
> the TSC is not monotonically increasing, then the guest will hang. How to
> prevent this?
No idea about that problem.
For migration, it usually works for me, but the clock of the guest starts
running way too fast.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: kvm live migration reliable?
2009-07-31 2:52 kvm live migration reliable? Kent Tong
2009-07-31 4:13 ` Stephane Bakhos
@ 2009-07-31 13:11 ` Anthony Liguori
1 sibling, 0 replies; 3+ messages in thread
From: Anthony Liguori @ 2009-07-31 13:11 UTC (permalink / raw)
To: Kent Tong; +Cc: kvm
Kent Tong wrote:
> Hi,
>
> I was wondering the kvm live migration function is reliable? I read that if
> the TSC is not monotonically increasing, then the guest will hang. How to
> prevent this?
>
KVM transfers the tsc as part of the CPU state so it will continue to
increase monotonically.
However, if you're migrating between two CPUs of different frequency,
the result will be that the TSC frequency will change. This could have
negative effects depends on how much the guest relies on the TSC. The
worst case would be if your guest was Linux and was using TSC as a time
source. You would likely see severe time drift.
A PV clock source (like KVM_CLOCK) helps this quite a bit.
Regards,
Anthony Liguori
> Thanks!
>
>
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^ permalink raw reply [flat|nested] 3+ messages in thread
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2009-07-31 2:52 kvm live migration reliable? Kent Tong
2009-07-31 4:13 ` Stephane Bakhos
2009-07-31 13:11 ` Anthony Liguori
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