From: Wanpeng Li <wanpen...@tencent.com> Using hypercall to send IPIs by one vmexit instead of one by one for xAPIC/x2APIC physical mode and one vmexit per-cluster for x2APIC cluster mode. Intel guest can enter x2apic cluster mode when interrupt remmaping is enabled in qemu, however, latest AMD EPYC still just supports xapic mode which can get great improvement by Exit-less IPIs. This patchset lets a guest which sends multicast IPIs at most can handle 128 vCPUs per hypercall on 64-bit machines and 64 vCPUs per hypercall on 32-bit machines.
Hardware: Xeon Skylake 2.5GHz, 2 sockets, 40 cores, 80 threads, the VM is 80 vCPUs, IPI microbenchmark(https://lkml.org/lkml/2017/12/19/141): x2apic cluster mode, vanilla Dry-run: 0, 2392199 ns Self-IPI: 6907514, 15027589 ns Normal IPI: 223910476, 251301666 ns Broadcast IPI: 0, 9282161150 ns Broadcast lock: 0, 8812934104 ns x2apic cluster mode, pv-ipi Dry-run: 0, 2449341 ns Self-IPI: 6720360, 15028732 ns Normal IPI: 228643307, 255708477 ns Broadcast IPI: 0, 7572293590 ns => 22% performance boost Broadcast lock: 0, 8316124651 ns x2apic physical mode, vanilla Dry-run: 0, 3135933 ns Self-IPI: 8572670, 17901757 ns Normal IPI: 226444334, 255421709 ns Broadcast IPI: 0, 19845070887 ns Broadcast lock: 0, 19827383656 ns x2apic physical mode, pv-ipi Dry-run: 0, 2446381 ns Self-IPI: 6788217, 15021056 ns Normal IPI: 219454441, 249583458 ns Broadcast IPI: 0, 7806540019 ns => 154% performance boost Broadcast lock: 0, 9143618799 ns Cc: Paolo Bonzini <pbonz...@redhat.com> Cc: Radim Krčmář <rkrc...@redhat.com> Cc: Vitaly Kuznetsov <vkuzn...@redhat.com> Signed-off-by: Wanpeng Li <wanpen...@tencent.com> --- Documentation/virtual/kvm/hypercalls.txt | 17 ++++++++++++++ arch/x86/kvm/x86.c | 38 ++++++++++++++++++++++++++++++++ 2 files changed, 55 insertions(+) diff --git a/Documentation/virtual/kvm/hypercalls.txt b/Documentation/virtual/kvm/hypercalls.txt index a890529..912b877 100644 --- a/Documentation/virtual/kvm/hypercalls.txt +++ b/Documentation/virtual/kvm/hypercalls.txt @@ -121,3 +121,20 @@ compute the CLOCK_REALTIME for its clock, at the same instant. Returns KVM_EOPNOTSUPP if the host does not use TSC clocksource, or if clock type is different than KVM_CLOCK_PAIRING_WALLCLOCK. + +6. KVM_HC_SEND_IPI +------------------------ +Architecture: x86 +Status: active +Purpose: Hypercall used to send IPIs. + +a0: ipi_bitmap low 64 bits +a1: ipi_bitmap high 64 bits +a2: the lowest APIC ID in bitmap +a3: APIC ICR + +The hypercall lets a guest send multicast IPIs at most can handle +128 vCPUs per hypercall on 64-bit machines and 64 vCPUs per hypercall +on 32-bit machines. + +Returns 0 if successfully delivery the IPIs and 1 if discarded. diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 2b812b3..016c7e2 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -6691,6 +6691,41 @@ static void kvm_pv_kick_cpu_op(struct kvm *kvm, unsigned long flags, int apicid) kvm_irq_delivery_to_apic(kvm, NULL, &lapic_irq, NULL); } +/* + * Return 0 if successfully added and 1 if discarded. + */ +static int kvm_pv_send_ipi(struct kvm *kvm, unsigned long ipi_bitmap_low, + unsigned long ipi_bitmap_high, int min, int vector, int op_64_bit) +{ + int i; + struct kvm_apic_map *map; + struct kvm_vcpu *vcpu; + struct kvm_lapic_irq irq = { + .delivery_mode = APIC_DM_FIXED, + .vector = vector, + }; + + rcu_read_lock(); + map = rcu_dereference(kvm->arch.apic_map); + + for_each_set_bit(i, &ipi_bitmap_low, BITS_PER_LONG) { + vcpu = map->phys_map[min + i]->vcpu; + if (!kvm_apic_set_irq(vcpu, &irq, NULL)) + return 1; + } + + if (op_64_bit) { + for_each_set_bit(i, &ipi_bitmap_high, BITS_PER_LONG) { + vcpu = map->phys_map[min + i + BITS_PER_LONG]->vcpu; + if (!kvm_apic_set_irq(vcpu, &irq, NULL)) + return 1; + } + } + + rcu_read_unlock(); + return 0; +} + void kvm_vcpu_deactivate_apicv(struct kvm_vcpu *vcpu) { vcpu->arch.apicv_active = false; @@ -6739,6 +6774,9 @@ int kvm_emulate_hypercall(struct kvm_vcpu *vcpu) case KVM_HC_CLOCK_PAIRING: ret = kvm_pv_clock_pairing(vcpu, a0, a1); break; + case KVM_HC_SEND_IPI: + ret = kvm_pv_send_ipi(vcpu->kvm, a0, a1, a2, a3, op_64_bit); + break; #endif default: ret = -KVM_ENOSYS; -- 2.7.4
