• Wanpeng Li's avatar
    KVM: X86: Implement "send IPI" hypercall · 4180bf1b
    Wanpeng Li authored
    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: default avatarWanpeng Li <wanpengli@tencent.com>
    Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
    4180bf1b
kvm_host.h 44 KB