Re: [PATCH RFC] kvm: enable irq injection from interrupt context

[Michael S. Tsirkin]

On Thu, Sep 16, 2010 at 12:13:32PM +0200, Gleb Natapov wrote:
> On Thu, Sep 16, 2010 at 11:53:10AM +0200, Michael S. Tsirkin wrote:
> > On Thu, Sep 16, 2010 at 11:46:03AM +0200, Avi Kivity wrote:
> > >  On 09/16/2010 11:25 AM, Gleb Natapov wrote:
> > > >>
> > > >>  MSI only appeared in rhel6, older guests still use level interrupts.
> > > >So they are already slow for other reasons.
> > > >
> > > 
> > > Exactly, for example they need to exit to userspace to ack the
> > > interrupt.  That's far slower than the workqueue.
> > 
> > Well, this is not exactly comparable: you might get
> > same irq asserted multiple times and only deasserted once.
> > 
> Are we talking about level interrupts? Why would you assert level
> triggered interrupt multiple times before deasserting it?

User of irqfd has no way to know what current interrupt level is.
So it has to keep asserting.

> --
> 			Gleb.
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