Re: [PATCH 18/15] kvm: Replace vcpu->swait with rcuwait

[Peter Zijlstra]

On Sun, Mar 22, 2020 at 09:33:17AM -0700, Davidlohr Bueso wrote:
> On Fri, 20 Mar 2020, Peter Zijlstra wrote:
> 
> > On Fri, Mar 20, 2020 at 01:55:26AM -0700, Davidlohr Bueso wrote:
> > > -	swait_event_interruptible_exclusive(*wq, ((!vcpu->arch.power_off) &&
> > > -				       (!vcpu->arch.pause)));
> > > +	rcuwait_wait_event(*wait,
> > > +			   (!vcpu->arch.power_off) && (!vcpu->arch.pause),
> > > +			   TASK_INTERRUPTIBLE);
> > 
> > > -	for (;;) {
> > > -		prepare_to_swait_exclusive(&vcpu->wq, &wait, TASK_INTERRUPTIBLE);
> > > -
> > > -		if (kvm_vcpu_check_block(vcpu) < 0)
> > > -			break;
> > > -
> > > -		waited = true;
> > > -		schedule();
> > > -	}
> > > -
> > > -	finish_swait(&vcpu->wq, &wait);
> > > +	rcuwait_wait_event(&vcpu->wait,
> > > +			   (block_check = kvm_vcpu_check_block(vcpu)) < 0,
> > > +			   TASK_INTERRUPTIBLE);
> > 
> > Are these yet more instances that really want to be TASK_IDLE ?
> 
> Hmm probably as it makes sense for a blocked vcpu not to be contributing to
> the loadavg. So if this is the only reason to use interruptible, then yes we
> ought to change it.
> 
> However, I'll make this a separate patch, given this (ab)use isn't as obvious
> as the PS3 case, which is a kthread and therefore signals are masked.

The thing that was a dead give-away was that the return value of the
interruptible wait wasn't used.