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

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Message-ID: <alpine.DEB.1.10.0905070944410.31280@makko.or.mcafeemobile.com>
Date:	Thu, 7 May 2009 09:44:55 -0700 (PDT)
From:	Davide Libenzi <davidel@...ilserver.org>
To:	Avi Kivity <avi@...hat.com>
cc:	Gregory Haskins <ghaskins@...ell.com>, viro@...IV.linux.org.uk,
	kvm@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [KVM PATCH v4 2/2] kvm: add support for irqfd via eventfd-notification
 interface

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


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