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

Jim Mattson
2020-06-19T18:50:12Z

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?