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

Marcelo Tosatti
2010-11-16T18:11:20Z

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.