diff options
| author | Wanpeng Li <wanpengli@tencent.com> | 2018-07-23 08:39:54 +0200 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2018-08-06 17:59:20 +0200 |
| commit | 4180bf1b655a791a0a6ef93a2ffffc762722c782 (patch) | |
| tree | b15142899c6343af5a3adf015d0528277820748c /Documentation | |
| parent | KVM/x86: Move X86_CR4_OSXSAVE check into kvm_valid_sregs() (diff) | |
| download | linux-4180bf1b655a791a0a6ef93a2ffffc762722c782.tar.xz linux-4180bf1b655a791a0a6ef93a2ffffc762722c782.zip | |
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>
Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/virtual/kvm/cpuid.txt | 4 | ||||
| -rw-r--r-- | Documentation/virtual/kvm/hypercalls.txt | 20 |
2 files changed, 24 insertions, 0 deletions
diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/kvm/cpuid.txt index ab022dcd0911..97ca1940a0dc 100644 --- a/Documentation/virtual/kvm/cpuid.txt +++ b/Documentation/virtual/kvm/cpuid.txt @@ -62,6 +62,10 @@ KVM_FEATURE_ASYNC_PF_VMEXIT || 10 || paravirtualized async PF VM exit || || can be enabled by setting bit 2 || || when writing to msr 0x4b564d02 ------------------------------------------------------------------------------ +KVM_FEATURE_PV_SEND_IPI || 11 || guest checks this feature bit + || || before using paravirtualized + || || send IPIs. +------------------------------------------------------------------------------ KVM_FEATURE_CLOCKSOURCE_STABLE_BIT || 24 || host will warn if no guest-side || || per-cpu warps are expected in || || kvmclock. diff --git a/Documentation/virtual/kvm/hypercalls.txt b/Documentation/virtual/kvm/hypercalls.txt index a890529c63ed..da24c138c8d1 100644 --- a/Documentation/virtual/kvm/hypercalls.txt +++ b/Documentation/virtual/kvm/hypercalls.txt @@ -121,3 +121,23 @@ compute the CLOCK_REALTIME for its clock, at the same instant. Returns KVM_EOPNOTSUPP if the host does not use TSC clocksource, or if clock type is different than KVM_CLOCK_PAIRING_WALLCLOCK. + +6. KVM_HC_SEND_IPI +------------------------ +Architecture: x86 +Status: active +Purpose: Send IPIs to multiple vCPUs. + +a0: lower part of the bitmap of destination APIC IDs +a1: higher part of the bitmap of destination APIC IDs +a2: the lowest APIC ID in bitmap +a3: APIC ICR + +The hypercall lets a guest send multicast IPIs, with at most 128 +128 destinations per hypercall in 64-bit mode and 64 vCPUs per +hypercall in 32-bit mode. The destinations are represented by a +bitmap contained in the first two arguments (a0 and a1). Bit 0 of +a0 corresponds to the APIC ID in the third argument (a2), bit 1 +corresponds to the APIC ID a2+1, and so on. + +Returns the number of CPUs to which the IPIs were delivered successfully. |