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

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Message-ID: <20100916154326.GL3008@redhat.com>
Date:	Thu, 16 Sep 2010 17:43:26 +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 05:24:11PM +0200, Michael S. Tsirkin wrote:
> On Thu, Sep 16, 2010 at 04:51:17PM +0200, Gleb Natapov wrote:
> > > > What for? Device emulation should do de-assert.
> > > 
> > > Sorry, but at this point I have no idea what you call device emulation.
> > The same thing everyone calls device emulation. In case of virtio-net it
> > is in hw/virtio-net.c. If vhost-net is in use device emulation is split
> > between userspace and kernel, but it is still just device emulation.
> 
> 
> case in point, virtio net does not know about pci at all,
> so it can not deassert.
> 
I don't see what PCI has to do with it. virtio-net device implementation is
split between several files. virtio-net/virtio-ring/virtio-pci. All of
them still implement one emulated device. Whoever implemented virtio-net
initially decided to put irq ack register into PCI config space, so code
that does de-assert is in virtio-pci, but it is still part of emulated
device.

> > > qemu has code to de-assert. vhost has code to assert.
> > Good. So qemu will de-assert. So what do you mean by
> > "KVM would need to find all irqfd objects mapped to gsi and notify
> > them on deassert"
> > 
> > > I would like to optimize level interrupts and stop driving
> > > scheduler insane if at all possible.
> > > 
> > Worthy goal. Do it in irqfd. Irqfd shouldn't call kvm_set_irq() if irq
> > level hasn't changed.
> 
> Right. Then it needs to know about deasserts. It does not get this
Dessert should be done by qemu writing 0 into irqfd. Assertion and
de-assertion should be done through irqfd.

> information, so when kvm gets deassert ioctl it should
> locate irqfd object and set level to 0.
> See?
No.

--
			Gleb.
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