linux-kernel - [PATCH 2/2] KVM: LAPIC: micro-optimize fixed mode ipi delivery

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Date:   Sat,  9 Nov 2019 15:05:35 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>
Subject: [PATCH 2/2] KVM: LAPIC: micro-optimize fixed mode ipi delivery

From: Wanpeng Li <wanpengli@...cent.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@...cent.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