Re: [Qemu-devel] Rethinking missed tick catchup

[Clemens Kolbitsch]

> On 2012-09-12 15:54, Anthony Liguori wrote:
>>
>> Hi,
>>
>> We've been running into a lot of problems lately with Windows guests and
>> I think they all ultimately could be addressed by revisiting the missed
>> tick catchup algorithms that we use.  Mike and I spent a while talking
>> about it yesterday and I wanted to take the discussion to the list to
>> get some additional input.
>>
>> Here are the problems we're seeing:
>>
>> 1) Rapid reinjection can lead to time moving faster for short bursts of
>>    time.  We've seen a number of RTC watchdog BSoDs and it's possible
>>    that at least one cause is reinjection speed.
>>
>> 2) When hibernating a host system, the guest gets is essentially paused
>>    for a long period of time.  This results in a very large tick catchup
>>    while also resulting in a large skew in guest time.
>>
>>    I've gotten reports of the tick catchup consuming a lot of CPU time
>>    from rapid delivery of interrupts (although I haven't reproduced this
>>    yet).

Guys,

not much that I can contribute to solving the problem, but I have a
bunch of VMs where this happens _every_ time I resume a snapshot (but
without hibernating). In case this could be a connected problem and
you need help testing a patch, I'm more than happy to help.

-Clemens