kvm: set irq affinity for assigned devices

To forward an interrupt to a vcpu that runs on a host cpu different from the current one,
we need an ipi which likely will cost us as much as delivering the interrupt directly to that cpu would.

So it seems to make sense to set irq affinity hint to point there, irq balancer can then take this into accound and balance interrupts accordingly.

This is what this patchset does.
Note: it might make sense to optimize the gsi lookups here for the msi case, using rcu, the way we did for eventfd. But that's a subject for another patch.

Testing shows that with irqbalance running this performs basically the same as manual numa pinning.

This patch applies to 3.2 or linux-next.

Changes from v1:
Address comments by Alex Williamson and Marcelo Tosatti:
- Fold in v2 patch from [email protected]:
fix affinity for lowest priority setups,
- Disable automatic affinity for round robin setups.
- Fix compiler warnings.
- Fix a checkpatch warning.
- Clear hint before free irq for MSI/INTx.

Michael S. Tsirkin (2):
kvm: pass host irq number to set irq calls
kvm: set affinity hint for assigned device msi

 arch/x86/kvm/i8254.c     |    4 ++--
 arch/x86/kvm/lapic.c     |    2 +-
 arch/x86/kvm/x86.c       |    2 +-
 include/linux/kvm_host.h |    7 ++++---
 virt/kvm/assigned-dev.c  |   14 +++++++++-----
 virt/kvm/eventfd.c       |    7 ++++---
 virt/kvm/ioapic.c        |    2 +-
 virt/kvm/ioapic.h        |    2 +-
 virt/kvm/irq_comm.c      |   43 ++++++++++++++++++++++++++++++++++---------
 9 files changed, 57 insertions(+), 26 deletions(-)

1.7.8.2.325.g247f9