Re: [PATCH v4 0/9] KVM: Improve IRQ assignment for device passthrough

[Marcelo Tosatti <mtosatti@redhat.com>]

On Mon, Nov 08, 2010 at 12:21:44PM +0100, Jan Kiszka wrote:
> Nine patches (yeah, it's getting more and more) to improve "classic"
> device assigment /wrt IRQs. Highlight is the last one that resolves the
> host IRQ sharing issue for all PCI 2.3 devices. Quite essential when
> passing non-MSI-ready devices like many USB host controllers.
> 
> As there were concerns regarding the overhead of IRQ masking via the PCI
> config space, I did some micro-benchmarks. Well, the concerns are valid:
> 
> disable_irq_nosync:           ~600 cycles
> pci_2_3_irq_check_and_mask:  ~6000 cycles (EHCI)
>                             ~22000 cycles (AR9287, with peaks >100000)
> 
> Specifically the varying impact of the device like in the Atheros case
> is worrying (this device is actually known to cause horrible latencies
> to the host, but who knows what other devices do). So I decided to go
> with PCI-2.3 masking as default off in the to-be-sent qemu-kvm patch.
> Maybe something to consider vor VFIO as well.

Looks fine to me. Michael, Alex? 

Also needs a rebase.