Re: [Xen-devel] [PATCH 1/3] xen/arm: introduce xen_read_wallclock

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Mon, 9 Nov 2015, Arnd Bergmann wrote:
> On Monday 09 November 2015 13:53:30 Stefano Stabellini wrote:
> > On Fri, 6 Nov 2015, Arnd Bergmann wrote:
> > > I'm not quite sure about how the split between pvclock_wall_clock and
> > > the delta works. Normally I'd expect that pvclock_wall_clock is the 
> > > wallclock
> > > time as it was at boot, while delta is the number of expired nanoseconds
> > > since boot. However it is unclear why the latter has a longer range
> > > (539 years starting at boot, rather than 126 years starting in 1970).
> > 
> > Actually we already have a sec overflow field in struct shared_info on
> > the hypervisor side, called wc_sec_hi. I just need to make use of it in
> > Linux. See:
> > 
> > http://xenbits.xen.org/gitweb/?p=xen.git;a=blob_plain;f=xen/include/public/xen.h;hb=HEAD
> > 
> > Thanks for raising my attention to the problem,
> 
> Sounds good for Xen on ARM. This same interface is also used on
> KVM, right? Does the extension also work there?

It doesn't look like it (see arch/x86/kvm/x86.c:kvm_write_wall_clock).

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