On 11/16/2010 08:26 PM, Jan Kiszka wrote:
Am 16.11.2010 17:55, Marcelo Tosatti wrote: > 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. I think Avi wanted to explore possibilities to avoid host_pci_2_3=on|off by switching between both modes on demand. I've some ideas, but still need to look into design details. Given that this would have impact on the ABI, I guess we better wait with merging 9/9.
Indeed.
Moreover, Avi preferred to skip the srcu conversion and run with a simply lock across kvm_set_irq (just like we do now).
Yes. It was predicated on agreeing that deferring broadcast/multicast IPIs to a workqueue is possible.
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