Re: [PATCH v4 00/10] VM Power Management

[Thomas Monjalon <thomas.monjalon-pdR9zngts4EAvxtiuMwx3w@public.gmane.org>]

2014-12-09 18:35, Paolo Bonzini:
> >>>> Did you make any progress in Qemu/KVM community?
> >>>> We need to be sync'ed up with them to be sure we share the same goal.
> >>>> I want also to avoid using a solution which doesn't fit with their
> >>>> plan.
> >>>> Remember that we already had this problem with ivshmem which was
> >>>> planned to be dropped.
> >>> 
> >>> Unfortunately, I have not yet received any feedback:
> >>> http://lists.nongnu.org/archive/html/qemu-devel/2014-11/msg01103.html
> >>
> >> Just to add to what Alan said above, this capability does not exist in
> >> qemu at the moment, and based on there having been no feedback on th
> >> qemu mailing list so far, I think it's reasonable to assume that it
> >> will not be implemented in the immediate future. The VM Power
> >> Management feature has also been designed to allow easy migration to a
> >> qemu-based solution when this is supported in future. Therefore, I'd
> >> be in favour of accepting this feature into DPDK now.
> >>
> >> It's true that the implementation is a work-around, but there have
> >> been similar cases in DPDK in the past. One recent example that comes
> >> to mind is userspace vhost. The original implementation could also be
> >> considered a work-around, but it met the needs of many in the
> >> community. Now, with support for vhost-user in qemu 2.1, that
> >> implementation is being improved. I'd see VM Power Management
> >> following a similar path when this capability is supported in qemu.
> 
> I wonder if this might be papering over a bug in the host cpufreq
> driver.  If the guest is not doing much and leaving a lot of idle CPU
> time, the host should scale down the frequency of that CPU.  In the case
> of pinned VCPUs this should really "just work".  What is the problem
> that is being solved?
> 
> Paolo

Alan, Pablo, please could you explain your logic with VM power management?

-- 
Thomas