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

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Message-ID: <20100916101332.GW3008@redhat.com>
Date:	Thu, 16 Sep 2010 12:13:32 +0200
From:	Gleb Natapov <gleb@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] kvm: enable irq injection from interrupt context

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?

--
			Gleb.
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