linux-kernel - Re: [PATCH RFC] kvm: fast-path msi injection with irqfd

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Date:	Thu, 18 Nov 2010 15:20:27 +0200
From:	"Michael S. Tsirkin" <mst@...hat.com>
To:	Gleb Natapov <gleb@...hat.com>
Cc:	Avi Kivity <avi@...hat.com>, Marcelo Tosatti <mtosatti@...hat.com>,
	Xiao Guangrong <xiaoguangrong@...fujitsu.com>,
	Gregory Haskins <ghaskins@...ell.com>,
	Chris Lalancette <clalance@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH RFC] kvm: fast-path msi injection with irqfd

On Thu, Nov 18, 2010 at 03:14:53PM +0200, Gleb Natapov wrote:
> On Thu, Nov 18, 2010 at 03:03:37PM +0200, Michael S. Tsirkin wrote:
> > > >+static inline void kvm_irq_routing_update(struct kvm *kvm,
> > > >+					  struct kvm_irq_routing_table *irq_rt)
> > > >+{
> > > >+	rcu_assign_pointer(kvm->irq_routing, irq_rt);
> > > >+}
> > > >+
> > > >  static inline int kvm_ioeventfd(struct kvm *kvm, struct kvm_ioeventfd *args)
> > > >  {
> > > >  	return -ENOSYS;
> > > 
> > > Apart from these minor issues, looks good.
> > 
> > 
> > Something we should consider improving is the loop over all VCPUs that
> > kvm_irq_delivery_to_apic invokes.  I think that (for non-broadcast
> > interrupts) it should be possible to precompute an store the CPU
> > in question as part of the routing entry.
> > 
> > Something for a separate patch ... comments?
> > 
> I do not think this info should be part of routing entry. Routing entry
> is more about describing wires on the board.

Not for msi. kvm_kernel_irq_routing_entry seems to just keep an
address/data pair in that case. So

	union {
		struct {
			unsigned irqchip;
			unsigned pin;
		} irqchip;
		struct msi_msg msi;
	};

would become

	union {
		struct {
			unsigned irqchip;
			unsigned pin;
		} irqchip;
		struct {
			struct msi_msg msi;
			struct kvm_vpcu *dest;
		} msi;
	};

or something like this.

> Other then that
> this is a good idea that, IIRC, we already discussed once.
> 
> --
> 			Gleb.
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