Re: [PATCH/RFC] KVM: halt_polling: provide a way to qualify wakeups during poll

[Cornelia Huck <cornelia.huck@de.ibm.com>]

On Tue, 3 May 2016 15:50:25 +0800
Wanpeng Li <kernellwp@gmail.com> wrote:

> 2016-05-02 18:42 GMT+08:00 Christian Borntraeger <borntraeger@de.ibm.com>:
> [...]
> > Some wakeups should not be considered a sucessful poll. For example on
> > s390 I/O interrupts are usually floating, which means that _ALL_ CPUs
> > would be considered runnable - letting all vCPUs poll all the time for
> > transactional like workload, even if one vCPU would be enough.
> > This can result in huge CPU usage for large guests.
> > This patch lets architectures provide a way to qualify wakeups if they
> > should be considered a good/bad wakeups in regard to polls.
> >
> > For s390 the implementation will fence of halt polling for anything but
> > known good, single vCPU events. The s390 implementation for floating
> > interrupts does a wakeup for one vCPU, but the interrupt will be delivered
> > by whatever CPU comes first. To limit the halt polling we only mark the
> 
> If the floating interrupt means that the 'CPU comes first' will
> deliver the interrupt to all vCPUs?

Floating interrupt on s390 means "deliver on any vcpu that matches the
criteria, but only on one".