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 v3 -> v4: * offset algorithm w/ __uint128_t to scale to higher APIC IDs * remove num_possible_cpus limit * pass op_64_bit to check bitmap size * better describe hypercall layout v2 -> v3: * rename ipi_mask_done to irq_restore_exit, __send_ipi_mask return int instead of bool * fix build errors reported by 0day * split patches, nothing change v1 -> v2: * sparse apic id > 128, or any other errors, fallback to original apic hooks * have two bitmask arguments so that one hypercall handles 128 vCPUs * fix KVM_FEATURE_PV_SEND_IPI doc * document hypercall * fix NMI selftest fails * fix build errors reported by 0day Cc: Paolo Bonzini <pbonzini@xxxxxxxxxx> Cc: Radim Krčmář <rkrcmar@xxxxxxxxxx> Cc: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> Wanpeng Li (6): KVM: X86: Add kvm hypervisor init time platform setup callback KVM: X86: Implement PV IPIs in linux guest KVM: X86: Fallback to original apic hooks when bad happens KVM: X86: Implement PV IPIs send hypercall KVM: X86: Add NMI support to PV IPIs KVM: X86: Expose PV_SEND_IPI CPUID feature bit to guest Documentation/virtual/kvm/cpuid.txt | 4 ++ Documentation/virtual/kvm/hypercalls.txt | 17 +++++ arch/x86/include/uapi/asm/kvm_para.h | 1 + arch/x86/kernel/kvm.c | 111 +++++++++++++++++++++++++++++++ arch/x86/kvm/cpuid.c | 3 +- arch/x86/kvm/x86.c | 44 ++++++++++++ include/uapi/linux/kvm_para.h | 1 + 7 files changed, 180 insertions(+), 1 deletion(-) -- 2.7.4
