Re: [Xen-devel] S3 sleep in dom0 breaks dom0<->domU wallclock synchronization

[Jeremy Fitzhardinge <jeremy@xxxxxxxx>]

On 07/05/2010 03:43 PM, Joanna Rutkowska wrote:
>> But the S3 suspend/resume is unnoticed by all the domUs, so they don't
>> know that an enormous amount of time has passed in an instant?
>>     
> Correct. I don't think DomU are notified in any way about system suspend
> -- at least nothing is in the dmesg/messages logs.
>
> BTW: wouldn't it be good to actually notify them? Consider e.g. DomU
> that has some device assigned to it (say a NIC) -- if we emulated S3
> suspend/resume for this DomU, there is a hope it would properly
> suspend/reinitialize the NIC, wouldn't it?
>   

I guess?  That implies some kind of PV S3 suspend and resume event to
feed into the dom U's device model.  What does 2.6.18-xen do?

As far as time goes, I think it makes most sense to try and resuse as
much of the existing kernel machinery as possible, rather than inventing
anything new.

I wonder if it makes sense to do a PV checkpoint-resume to PV domains on
host S3?

>> Does that affect all the guest clocks, or just wallclock?
>>
>>     
> Not sure if I understand your question -- what do you mean by "all guest
> clocks"? Like timers? They don't seem to be affected [*], as the apps
> run smoothly.
>   

I mean the other clocks you can real with clock_gettime(), such as
CLOCK_MONOTONIC or CLOCK_PROCESS_CPUTIME_ID, in addition to CLOCK_REALTIME.

    J

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