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https://github.com/AuxXxilium/linux_dsm_epyc7002.git
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4180bf1b65
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>
84 lines
4.7 KiB
Plaintext
84 lines
4.7 KiB
Plaintext
KVM CPUID bits
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Glauber Costa <glommer@redhat.com>, Red Hat Inc, 2010
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=====================================================
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A guest running on a kvm host, can check some of its features using
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cpuid. This is not always guaranteed to work, since userspace can
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mask-out some, or even all KVM-related cpuid features before launching
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a guest.
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KVM cpuid functions are:
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function: KVM_CPUID_SIGNATURE (0x40000000)
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returns : eax = 0x40000001,
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ebx = 0x4b4d564b,
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ecx = 0x564b4d56,
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edx = 0x4d.
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Note that this value in ebx, ecx and edx corresponds to the string "KVMKVMKVM".
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The value in eax corresponds to the maximum cpuid function present in this leaf,
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and will be updated if more functions are added in the future.
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Note also that old hosts set eax value to 0x0. This should
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be interpreted as if the value was 0x40000001.
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This function queries the presence of KVM cpuid leafs.
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function: define KVM_CPUID_FEATURES (0x40000001)
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returns : ebx, ecx
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eax = an OR'ed group of (1 << flag), where each flags is:
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flag || value || meaning
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=============================================================================
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KVM_FEATURE_CLOCKSOURCE || 0 || kvmclock available at msrs
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|| || 0x11 and 0x12.
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------------------------------------------------------------------------------
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KVM_FEATURE_NOP_IO_DELAY || 1 || not necessary to perform delays
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|| || on PIO operations.
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------------------------------------------------------------------------------
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KVM_FEATURE_MMU_OP || 2 || deprecated.
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------------------------------------------------------------------------------
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KVM_FEATURE_CLOCKSOURCE2 || 3 || kvmclock available at msrs
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|| || 0x4b564d00 and 0x4b564d01
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------------------------------------------------------------------------------
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KVM_FEATURE_ASYNC_PF || 4 || async pf can be enabled by
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|| || writing to msr 0x4b564d02
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------------------------------------------------------------------------------
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KVM_FEATURE_STEAL_TIME || 5 || steal time can be enabled by
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|| || writing to msr 0x4b564d03.
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------------------------------------------------------------------------------
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KVM_FEATURE_PV_EOI || 6 || paravirtualized end of interrupt
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|| || handler can be enabled by writing
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|| || to msr 0x4b564d04.
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------------------------------------------------------------------------------
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KVM_FEATURE_PV_UNHALT || 7 || guest checks this feature bit
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|| || before enabling paravirtualized
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|| || spinlock support.
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------------------------------------------------------------------------------
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KVM_FEATURE_PV_TLB_FLUSH || 9 || guest checks this feature bit
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|| || before enabling paravirtualized
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|| || tlb flush.
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------------------------------------------------------------------------------
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KVM_FEATURE_ASYNC_PF_VMEXIT || 10 || paravirtualized async PF VM exit
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|| || can be enabled by setting bit 2
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|| || when writing to msr 0x4b564d02
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------------------------------------------------------------------------------
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KVM_FEATURE_PV_SEND_IPI || 11 || guest checks this feature bit
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|| || before using paravirtualized
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|| || send IPIs.
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------------------------------------------------------------------------------
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KVM_FEATURE_CLOCKSOURCE_STABLE_BIT || 24 || host will warn if no guest-side
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|| || per-cpu warps are expected in
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|| || kvmclock.
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------------------------------------------------------------------------------
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edx = an OR'ed group of (1 << flag), where each flags is:
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flag || value || meaning
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==================================================================================
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KVM_HINTS_REALTIME || 0 || guest checks this feature bit to
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|| || determine that vCPUs are never
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|| || preempted for an unlimited time,
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|| || allowing optimizations
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----------------------------------------------------------------------------------
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