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Diffstat (limited to 'Documentation/virtual/kvm/api.txt')
| -rw-r--r-- | Documentation/virtual/kvm/api.txt | 16 |
1 files changed, 10 insertions, 6 deletions
diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt index 10d48eb67da9..70f9c8bb1840 100644 --- a/Documentation/virtual/kvm/api.txt +++ b/Documentation/virtual/kvm/api.txt @@ -3683,27 +3683,31 @@ the definition of struct kvm_nested_state, see KVM_GET_NESTED_STATE. 4.116 KVM_(UN)REGISTER_COALESCED_MMIO -Capability: KVM_CAP_COALESCED_MMIO +Capability: KVM_CAP_COALESCED_MMIO (for coalesced mmio) + KVM_CAP_COALESCED_PIO (for coalesced pio) Architectures: all Type: vm ioctl Parameters: struct kvm_coalesced_mmio_zone Returns: 0 on success, < 0 on error -Coalesced mmio is a performance optimization that defers hardware +Coalesced I/O is a performance optimization that defers hardware register write emulation so that userspace exits are avoided. It is typically used to reduce the overhead of emulating frequently accessed hardware registers. -When a hardware register is configured for coalesced mmio, write accesses +When a hardware register is configured for coalesced I/O, write accesses do not exit to userspace and their value is recorded in a ring buffer that is shared between kernel and userspace. -Coalesced mmio is used if one or more write accesses to a hardware +Coalesced I/O is used if one or more write accesses to a hardware register can be deferred until a read or a write to another hardware register on the same device. This last access will cause a vmexit and userspace will process accesses from the ring buffer before emulating -it. That will avoid exiting to userspace on repeated writes to the -first register. +it. That will avoid exiting to userspace on repeated writes. + +Coalesced pio is based on coalesced mmio. There is little difference +between coalesced mmio and pio except that coalesced pio records accesses +to I/O ports. 5. The kvm_run structure ------------------------ |