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

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Message-ID: <4CE5257B.60206@redhat.com>
Date:	Thu, 18 Nov 2010 15:09:15 +0200
From:	Avi Kivity <avi@...hat.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	Marcelo Tosatti <mtosatti@...hat.com>,
	Gleb Natapov <gleb@...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 11/18/2010 03:03 PM, Michael S. Tsirkin wrote:
> >  >   int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level);
> >  >+int kvm_set_msi(struct kvm_kernel_irq_routing_entry *irq_entry, struct kvm *kvm,
> >  >+		int irq_source_id, int level);
> >
> >  No point in the level argument for an msi specific function.
>
> This is an existing function I made non-static.
> We have per-gsi callbacks so level is required there to match.

Right.

> I could add a wrapper I guess:
>
> int kvm_set_msi(struct kvm_kernel_irq_routing_entry *irq_entry, struct kvm *kvm,
> 		int irq_source_id, int level)
> {
> 	if (!level)
> 		return -1;
> 	return kvm_send_msi(irq_entry, kvm, irq_source_id);
> }
>
> This results in less code for irqfd but more code for ioctl injection
> ... is it worth it?

IMO not.

> >
> >  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?

Yes.  Either precompute, or compute on first use and cache.  Precompute 
is more realtime-friendly so I prefer it.

-- 
error compiling committee.c: too many arguments to function

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