Commits
Wanpeng Li committed 4180bf1b655
KVM: X86: Implement "send IPI" hypercall 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 send multicast IPIs, with at most 128 destinations per hypercall in 64-bit mode and 64 vCPUs per hypercall in 32-bit mode. 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 <pbonzini@redhat.com> Cc: Radim Krčmář <rkrcmar@redhat.com> Cc: Vitaly Kuznetsov <vkuznets@redhat.com> Signed-off-by: Wanpeng Li <wanpengli@tencent.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>