Re: [PATCH] cpuidle-haltpoll: Enable kvm guest polling when dedicated physical CPUs are available

[Marcelo Tosatti]

On Thu, Aug 01, 2019 at 06:54:49PM +0200, Paolo Bonzini wrote:
> On 01/08/19 18:51, Rafael J. Wysocki wrote:
> > On 8/1/2019 9:06 AM, Wanpeng Li wrote:
> >> From: Wanpeng Li <wanpengli@xxxxxxxxxxx>
> >>
> >> The downside of guest side polling is that polling is performed even
> >> with other runnable tasks in the host. However, even if poll in kvm
> >> can aware whether or not other runnable tasks in the same pCPU, it
> >> can still incur extra overhead in over-subscribe scenario. Now we can
> >> just enable guest polling when dedicated pCPUs are available.
> >>
> >> Cc: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> >> Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> >> Cc: Radim KrÄmÃÅ <rkrcmar@xxxxxxxxxx>
> >> Cc: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
> >> Signed-off-by: Wanpeng Li <wanpengli@xxxxxxxxxxx>
> > 
> > Paolo, Marcelo, any comments?
> 
> Yes, it's a good idea.
> 
> Acked-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> 
> Paolo

I think KVM_HINTS_REALTIME is being abused somewhat.
It has no clear meaning and used in different locations 
for different purposes.

For example, i think that using pv queued spinlocks and 
haltpoll is a desired scenario, which the patch below disallows.

Wanpeng Li, currently the driver does not autoload. So polling in 
the guest has to be enabled manually. Isnt that sufficient?