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Subject[PATCH v3 0/6] KVM: X86: Implement PV IPIs support
Date
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 PV IPIs. This patchset supports
PV IPIs for maximal 128 vCPUs VM, it is big enough for cloud environment
currently, supporting more vCPUs needs to introduce more complex logic,
in the future this might be extended if needed.

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

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@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>

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 | 6 ++
arch/x86/include/uapi/asm/kvm_para.h | 1 +
arch/x86/kernel/kvm.c | 101 +++++++++++++++++++++++++++++++
arch/x86/kvm/cpuid.c | 3 +-
arch/x86/kvm/x86.c | 42 +++++++++++++
include/uapi/linux/kvm_para.h | 1 +
7 files changed, 157 insertions(+), 1 deletion(-)

--
2.7.4

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