Re: [Xen-devel] Re: [PATCH 3/5] x86/pvclock: add vsyscall implementation

Avi Kivity
2009-10-14T12:34:28Z

On 10/14/2009 05:00 AM, Jeremy Fitzhardinge wrote:
>
>> So it's broken or disabled when that assumption is wrong? We could
>> easily fix that now. Might even reuse the pvclock structures.
>>
> Well, the kernel internally makes more or less the same assumption; the
> vsyscall clocksource is the same as the kernel's internal one. I think
> idea is that it just drops back to something like hpet if the tsc
> doesn't have very simple SMP characteristics.
>
> If the kernel could characterize the per-cpu properties of the tsc more
> accurately, then it could use the pvclock mechanism on native.
>

It does - that's how kvm implements pvclock on the host side. See
kvmclock_cpufreq_notifier() in arch/x86/kvm/x86.c.

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.