Re: [RFC] Paravirt timer for KVM

Glauber de Oliveira Costa
2007-10-15T17:52:02Z

On 10/15/07, Dong, Eddie <eddie.dong-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org> wrote:
>
> >>> 1) the PIT is periodic. a PV timer can offer a one shot
> >timer which
> >>> enables dynticks.
> >>>
> >>
> >> Obviously people have figured out how to do dynticks on real x86
> >> hardware, so I don't accept this reason. :)
> >>
> >
> >Using more advanced timers like the HPET.
> >
>
> I'd think there is no reason for virtual timer to be PIT like, which
> is mostly due to historic reason.
>
> If we need to make it close to native timer device, HPET is much
> better than PIT for virtual time to look like.
>

Besides of course, the fact that you'd still have to keep the PIT
timer around, for this same historical reason: It lives in an
emulation layer that can't make too much assumptions about what's
running on it, and it may well use the PIT exclusively. And we end up
with two code bases to maintain.

Obviously, as everything else, it's a trade-off. If the only benefit
of an HPET like timer is its programability, then the paravirt timer
solves this problem with less effort. If there are others, it might
well be worth it.

--
Glauber de Oliveira Costa.
"Free as in Freedom"
http://glommer.net

"The less confident you are, the more serious you have to act."