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Subject[PATCH 2/2] KVM: LAPIC: micro-optimize fixed mode ipi delivery
Date
From: Wanpeng Li <wanpengli@tencent.com>

After disabling mwait/halt/pause vmexits, RESCHEDULE_VECTOR and
CALL_FUNCTION_SINGLE_VECTOR etc IPI is one of the main remaining
cause of vmexits observed in product environment which can't be
optimized by PV IPIs. This patch is the follow-up on commit
0e6d242eccdb (KVM: LAPIC: Micro optimize IPI latency), to optimize
redundancy logic before fixed mode ipi is delivered in the fast
path.

- broadcast handling needs to go slow path, so the delivery mode repair
can be delayed to before slow path.
- self-IPI will not be intervened by hypervisor any more after APICv is
introduced and the boxes support APICv are popular now. In addition,
kvm_apic_map_get_dest_lapic() can handle the self-IPI, so there is no
need a shortcut for the non-APICv case.

Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
---
arch/x86/kvm/irq_comm.c | 6 +++---
arch/x86/kvm/lapic.c | 5 -----
2 files changed, 3 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c
index 8ecd48d..aa88156 100644
--- a/arch/x86/kvm/irq_comm.c
+++ b/arch/x86/kvm/irq_comm.c
@@ -52,15 +52,15 @@ int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src,
unsigned long dest_vcpu_bitmap[BITS_TO_LONGS(KVM_MAX_VCPUS)];
unsigned int dest_vcpus = 0;

+ if (kvm_irq_delivery_to_apic_fast(kvm, src, irq, &r, dest_map))
+ return r;
+
if (irq->dest_mode == 0 && irq->dest_id == 0xff &&
kvm_lowest_prio_delivery(irq)) {
printk(KERN_INFO "kvm: apic: phys broadcast and lowest prio\n");
irq->delivery_mode = APIC_DM_FIXED;
}

- if (kvm_irq_delivery_to_apic_fast(kvm, src, irq, &r, dest_map))
- return r;
-
memset(dest_vcpu_bitmap, 0, sizeof(dest_vcpu_bitmap));

kvm_for_each_vcpu(i, vcpu, kvm) {
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index b29d00b..ea936fa 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -951,11 +951,6 @@ bool kvm_irq_delivery_to_apic_fast(struct kvm *kvm, struct kvm_lapic *src,

*r = -1;

- if (irq->shorthand == APIC_DEST_SELF) {
- *r = kvm_apic_set_irq(src->vcpu, irq, dest_map);
- return true;
- }
-
rcu_read_lock();
map = rcu_dereference(kvm->arch.apic_map);

--
2.7.4
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