Re: [ RfC / patch ] kvmclock fixes

[Jeremy Fitzhardinge <jeremy@goop.org>]

Gerd Hoffmann wrote:
>   * Host: make kvm pv clock really compatible with xen pv clock.
>   * Guest/xen: factor out some xen clock code into a separate
>                source file (pvclock.[ch]), so kvm can reuse it.
>   * Guest/kvm: make kvm clock compatible with xen clock by using
>                the common code bits.
>   

I guess saving on code duplication is good...

> +cycle_t pvclock_clocksource_read(struct kvm_vcpu_time_info *src)
> +{
> +	struct pvclock_shadow_time *shadow = &get_cpu_var(shadow_time);
> +	cycle_t ret;
> +
> +	pvclock_get_time_values(shadow, src);
> +	ret = shadow->system_timestamp + pvclock_get_nsec_offset(shadow);
>   

You need to put this in a loop in case the system clock parameters 
change between the pvclock_get_time_values() and pvclock_get_nsec_offset().

How does kvm deal with suspend/resume with respect to time?  Is the 
"system" timestamp guaranteed to remain monotonic?  For Xen, I think 
we'll need to maintain an offset between the initial system timestamp 
and whatever it is after resuming.

    J

-------------------------------------------------------------------------
This SF.net email is sponsored by the 2008 JavaOne(SM) Conference 
Don't miss this year's exciting event. There's still time to save $100. 
Use priority code J8TL2D2. 
http://ad.doubleclick.net/clk;198757673;13503038;p?http://java.sun.com/javaone