Re: [PATCH 0/3] Pin the hrtimer used for VMX-preemption timer emulation

Paolo Bonzini
2020-06-19T22:52:58Z

On 19/06/20 20:49, Jim Mattson wrote:
> On Fri, May 8, 2020 at 1:36 PM Jim Mattson <jmattson@google.com> wrote:
>>
>> I'm still not entirely convinced that the Linux hrtimer can be used to
>> accurately emulate the VMX-preemption timer...
>
> It can't, for several reasons:
>
> 1) The conversion between wall-clock time and TSC frequency, based on
> tsc_khz, isn't precise enough.
> 2) The base clock for the hrtimer, CLOCK_MONOTONIC, can be slewed,
> whereas the TSC cannot.
> 3) The VMX-preemption timer is suspended during MWAIT; the hrtimer is not.
>
> Is there any reason that VMX-preemption timer emulation shouldn't just
> be a second client of the hv_timer, along with lapic timer emulation?

I don't think so, you'd just need logic to multiplex it.

Paolo