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

[Davidlohr Bueso]

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.

Thanks,
Davidlohr