Re: pv clock: kvm is incompatible with xen :-(

[Jeremy Fitzhardinge <jeremy@goop.org>]

Gerd Hoffmann wrote:
> Jeremy Fitzhardinge wrote:
>   
>> Xen could change the parameters in the instant after get_time_values(). 
>> That change could be as a result of suspend-resume, so the parameters
>> and the tsc could be wildly different.
>>     
>
> Ah, ok, forgot the rdtsc in the picture.  With that in mind I fully
> agree that the loop is needed.  I think kvm guests can even hit that one
> with the vcpu migrating to a different physical cpu, so we better handle
> it correctly ;)
>   

Yes, same with Xen.

>> Sure, but get_time_values() has several other callers.
>>     
>
> Not really.  There are only two calls, one in clocksource_read() and one
> in the init path.  The later is superfluous I think because
> clocksource_read() is the only user of the shadowed time info.
>   

Hm.  It doesn't look like shadow_time needs to be a static percpu at 
all.  It could just be a local to clocksource_read, I think.

    J

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