Re: kvm & dyntick

Ingo Molnar
2007-01-12T10:19:31Z

* Ingo Molnar <mingo-X9Un+BFzKDI@public.gmane.org> wrote:

> > dyntick-enabled guest:
> > - reduce the load on the host when the guest is idling
> > (currently an idle guest consumes a few percent cpu)
>
> yeah. KVM under -rt already works with dynticks enabled on both the
> host and the guest. (but it's more optimal to use a dedicated
> hypercall to set the next guest-interrupt)

using the dynticks code from the -rt kernel makes the overhead of an
idle guest go down by a factor of 10-15:

PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
2556 mingo 15 0 598m 159m 157m R 1.5 8.0 0:26.20 qemu

( for this to work on my system i have added a 'hyper' clocksource
hypercall API for KVM guests to use - this is needed instead of the
running-to-slowly TSC. )

Ingo