Re: [KVM PATCH v4 2/2] kvm: add support for irqfd via eventfd-notification interface

Davide Libenzi
2009-05-07T16:49:51Z

On Thu, 7 May 2009, Avi Kivity wrote:

> Davide Libenzi wrote:
> >
> > > What's your take on adding irq context safe callbacks to irqfd?
> > >
> > > To give some background here, we would like to use eventfd as a generic
> > > connector between components, so the components do not know about each
> > > other.
> > > So far eventfd successfully abstracts among components in the same
> > > process, in
> > > different processes, and in the kernel.
> > >
> > > eventfd_signal() can be safely called from irq context, and will wake up a
> > > waiting task. But in some cases, if the consumer is in the kernel, it may
> > > be
> > > able to consume the event from irq context, saving a context switch.
> > >
> > > So, will you consider patches adding this capability to eventfd?
> > >
> >
> > Maybe I got lost in the thread, but inside the kernel we have callback-based
> > wakeup since long time. This is what epoll uses, when hooking into the file*
> > f_op->poll() subsystem.
> > Did you mean something else?
> >
>
> Do you mean wait_queue_t::func?

Yes, it is since long time ago that a wakeup in Linux can lead either to a
real wakeup (in scheduler terms), or to a simple function call.
Isn't that enough?

- Davide