Re: [patch -rt 1/2] KVM: use simple waitqueue for vcpu->wq

Peter Zijlstra
2015-01-17T07:57:44Z

On Fri, Jan 16, 2015 at 11:48:46AM -0500, Steven Rostedt wrote:
> I notice everywhere you have a swait_wake_interruptible() but here. Is
> there a reason why?
>
> IIRC, Peter wants to make swait wakeup usage homogenous. That is, you
> either sleep in an interruptible state, or you don't. You can't mix and
> match it.
>
> Peter is that what you plan?

Yes, this is required for the single wakeup case to be bounded.

If you have both INTERRUPTIBLE and UNINTERRUPTIBLE waiters on a list,
and you were allowed to do INTERRUPTIBLE/UNINTERRUPTIBLE wakeups, the
wakeup would have to do O(n) iteration to find a matching waiter.

Seeing that the entire purpose of simple wait queues was to retain RT
properties, that's entirely retarded ;-)