Re: [PATCH RFC hack dont apply] intel_idle: support running within a VM

[Jacob Pan <jacob.jun.pan@linux.intel.com>]

On Sat, 30 Sep 2017 01:21:43 +0200
"Rafael J. Wysocki" <rafael@kernel.org> wrote:

> On Sat, Sep 30, 2017 at 12:01 AM, Michael S. Tsirkin <mst@redhat.com>
> wrote:
> > intel idle driver does not DTRT when running within a VM:
> > when going into a deep power state, the right thing to
> > do is to exit to hypervisor rather than to keep polling
> > within guest using mwait.
> >
> > Currently the solution is just to exit to hypervisor each time we go
> > idle - this is why kvm does not expose the mwait leaf to guests even
> > when it allows guests to do mwait.
> >
> > But that's not ideal - it seems better to use the idle driver to
> > guess when will the next interrupt arrive.  
> 
> The idle driver alone is not sufficient for that, though.
> 
I second that. Why try to solve this problem at vendor specific driver
level? perhaps just a pv idle driver that decide whether to vmexit
based on something like local per vCPU timer expiration? I guess we
can't predict other wake events such as interrupts.
e.g.
if (get_next_timer_interrupt() > kvm_halt_target_residency)
	vmexit
else
	poll

Jacob