[PATCH 0/5] KVM: x86: cleanup and minimal speedup for APICv

From: Paolo Bonzini
Date: Fri Oct 14 2016 - 14:23:17 EST

On some benchmarks (e.g. netperf with ioeventfd disabled), APICv
posted interrupts turn out to be slower than interrupt injection via

These patches save 40 cycles on kvm-unit-tests "inl" tests (1-2%), but I
suspect the effect is bigger on workloads that inject interrupts heavily.

Patches 1-2 are micro-optimization of the APICv vmentry code.

The interesting one is patch 3. The aim is for APICv to not use
KVM_REQ_EVENT at all for interrupts, therefore turning APICv's weakness
(having to look at PIR on every vmentry) into a strength (because
checking PIR.ON is cheaper than processing KVM_REQ_EVENT). I find that
the new code overall makes more sense than the old one, and I like that
more of the logic is contained within vmx_deliver_posted_interrupt and
vmx_sync_pir_to_irr. KVM_REQ_EVENT did protect from mistakes, so the new
code is more delicate, but I still prefer that to duct tape. :)

Patches 4 and 5 are other cleanups.


Paolo Bonzini (5):
KVM: x86: avoid atomic operations on APICv vmentry
KVM: x86: do not scan IRR twice on APICv vmentry
KVM: x86: do not use KVM_REQ_EVENT for APICv interrupt injection
KVM: x86: remove unnecessary sync_pir_to_irr
KVM: vmx: clear pending interrupts on KVM_SET_LAPIC

arch/x86/kvm/lapic.c | 45 +++++++++++++++++++++++++++++----------------
arch/x86/kvm/lapic.h | 4 ++--
arch/x86/kvm/vmx.c | 44 ++++++++++++++++++++++++++++++++------------
arch/x86/kvm/x86.c | 45 +++++++++++++++++++++++++--------------------
4 files changed, 88 insertions(+), 50 deletions(-)