Message ID | 20210618222709.1858088-6-jingzhangos@google.com (mailing list archive) |
---|---|

State | New, archived |

Headers | show |

Series | KVM statistics data fd-based binary interface | expand |

diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index e328caa35d6c..289ea7be696a 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -5034,7 +5034,6 @@ see KVM_XEN_VCPU_SET_ATTR above. The KVM_XEN_VCPU_ATTR_TYPE_RUNSTATE_ADJUST type may not be used with the KVM_XEN_VCPU_GET_ATTR ioctl. - 4.131 KVM_GET_SREGS2 ------------------ @@ -5081,6 +5080,195 @@ Writes special registers into the vcpu. See KVM_GET_SREGS2 for the data structures. This ioctl (when supported) replaces the KVM_SET_SREGS. +4.133 KVM_GET_STATS_FD +---------------------- + +:Capability: KVM_CAP_STATS_BINARY_FD +:Architectures: all +:Type: vm ioctl, vcpu ioctl +:Parameters: none +:Returns: statistics file descriptor on success, < 0 on error + +Errors: + + ====== ====================================================== + ENOMEM if the fd could not be created due to lack of memory + EMFILE if the number of opened files exceeds the limit + ====== ====================================================== + +The file descriptor can be used to read VM/vCPU statistics data in binary +format. Please be aware that it is not guaranteed that the four blocks are +adjacent, that's why offset fields are included in the Header. But the +order of the four blocks are guaranteed and there is no overlap between any +two blocks. +And all four blocks are aligned with 64 bits in the file. +The file data is organized into three blocks as below: ++-------------+ +| Header | ++-------------+ ++-------------+ +| id string | ++-------------+ ++-------------+ +| Descriptors | ++-------------+ ++-------------+ +| Stats Data | ++-------------+ + +The Header block is always at the start of the file. It is only needed to be +read one time for the lifetime of the file descriptor. +It is in the form of ``struct kvm_stats_header`` as below:: + + struct kvm_stats_header { + __u32 flags; + __u32 name_size; + __u32 num_desc; + __u32 id_offset; + __u32 desc_offset; + __u32 data_offset; + }; + +The ``flags`` field is not used at the moment. It is always read as 0. + +The ``name_size`` field is the size (in byte) of the statistics name string +(including trailing '\0') appended to the end of every statistics descriptor. +It also is the size of id string block. + +The ``num_desc`` field is the number of statistics. + +The ``id_offset`` field is the offset of the id string from the start of the +file indicated by the file descriptor. It is a multiple of 8. + +The ``desc_offset`` field is the offset of the Descriptors block from the start +of the file indicated by the file descriptor. It is a multiple of 8. + +The ``data_offset`` field is the offset of the Stats Data block from the start +of the file indicated by the file descriptor. It is a multiple of 8. + +The id string is a '\0' terminated string which identifies the corresponding +KVM statistics. For VM statistics, it is in the form of "kvm-{kvm pid}", like +"kvm-12345". For VCPU statistics, it is in the form of +"kvm-{kvm pid}/vcpu-{vcpu id}", like "kvm-12345/vcpu-12". +The size of id string block is indicated by the ``name_size`` field in Header. + +The Descriptors block is only needed to be read once for the lifetime of the +file descriptor. It is an array of ``struct kvm_stats_desc`` as shown in +below code block:: + + #define KVM_STATS_TYPE_SHIFT 0 + #define KVM_STATS_TYPE_MASK (0xF << KVM_STATS_TYPE_SHIFT) + #define KVM_STATS_TYPE_CUMULATIVE (0x0 << KVM_STATS_TYPE_SHIFT) + #define KVM_STATS_TYPE_INSTANT (0x1 << KVM_STATS_TYPE_SHIFT) + #define KVM_STATS_TYPE_PEAK (0x2 << KVM_STATS_TYPE_SHIFT) + #define KVM_STATS_TYPE_MAX KVM_STATS_TYPE_PEAK + + #define KVM_STATS_UNIT_SHIFT 4 + #define KVM_STATS_UNIT_MASK (0xF << KVM_STATS_UNIT_SHIFT) + #define KVM_STATS_UNIT_NONE (0x0 << KVM_STATS_UNIT_SHIFT) + #define KVM_STATS_UNIT_BYTES (0x1 << KVM_STATS_UNIT_SHIFT) + #define KVM_STATS_UNIT_SECONDS (0x2 << KVM_STATS_UNIT_SHIFT) + #define KVM_STATS_UNIT_CYCLES (0x3 << KVM_STATS_UNIT_SHIFT) + #define KVM_STATS_UNIT_MAX KVM_STATS_UNIT_CYCLES + + #define KVM_STATS_BASE_SHIFT 8 + #define KVM_STATS_BASE_MASK (0xF << KVM_STATS_BASE_SHIFT) + #define KVM_STATS_BASE_POW10 (0x0 << KVM_STATS_BASE_SHIFT) + #define KVM_STATS_BASE_POW2 (0x1 << KVM_STATS_BASE_SHIFT) + #define KVM_STATS_BASE_MAX KVM_STATS_BASE_POW2 + + struct kvm_stats_desc { + __u32 flags; + __s16 exponent; + __u16 size; + __u32 offset; + __u32 unused; + char name[]; + }; + +The ``flags`` field contains the type and unit of the statistics data described +by this descriptor. Its endianness is CPU native. +The following flags are supported: + +Bits 0-3 of ``flags`` encode the type: + * ``KVM_STATS_TYPE_CUMULATIVE`` + The statistics data is cumulative. The value of data can only be increased. + Most of the counters used in KVM are of this type. + The corresponding ``size`` field for this type is always 1. + All cumulative statistics data are read/write. + * ``KVM_STATS_TYPE_INSTANT`` + The statistics data is instantaneous. Its value can be increased or + decreased. This type is usually used as a measurement of some resources, + like the number of dirty pages, the number of large pages, etc. + All instant statistics are read only. + The corresponding ``size`` field for this type is always 1. + * ``KVM_STATS_TYPE_PEAK`` + The statistics data is peak, which is used as read/write instant statistics. + The corresponding ``size`` field for this type is always 1. + +Bits 4-7 of ``flags`` encode the unit: + * ``KVM_STATS_UNIT_NONE`` + There is no unit for the value of statistics data. This usually means that + the value is a simple counter of an event. + * ``KVM_STATS_UNIT_BYTES`` + It indicates that the statistics data is used to measure memory size, in the + unit of Byte, KiByte, MiByte, GiByte, etc. The unit of the data is + determined by the ``exponent`` field in the descriptor. The + ``KVM_STATS_BASE_POW2`` flag is valid in this case. The unit of the data is + determined by ``pow(2, exponent)``. For example, if value is 10, + ``exponent`` is 20, which means the unit of statistics data is MiByte, we + can get the statistics data in the unit of Byte by + ``value * pow(2, exponent) = 10 * pow(2, 20) = 10 MiByte`` which is + 10 * 1024 * 1024 Bytes. + * ``KVM_STATS_UNIT_SECONDS`` + It indicates that the statistics data is used to measure time/latency, in + the unit of nanosecond, microsecond, millisecond and second. The unit of the + data is determined by the ``exponent`` field in the descriptor. The + ``KVM_STATS_BASE_POW10`` flag is valid in this case. The unit of the data + is determined by ``pow(10, exponent)``. For example, if value is 2000000, + ``exponent`` is -6, which means the unit of statistics data is microsecond, + we can get the statistics data in the unit of second by + ``value * pow(10, exponent) = 2000000 * pow(10, -6) = 2 seconds``. + * ``KVM_STATS_UNIT_CYCLES`` + It indicates that the statistics data is used to measure CPU clock cycles. + The ``KVM_STATS_BASE_POW10`` flag is valid in this case. For example, if + value is 200, ``exponent`` is 4, we can get the number of CPU clock cycles + by ``value * pow(10, exponent) = 200 * pow(10, 4) = 2000000``. + +Bits 8-11 of ``flags`` encode the base: + * ``KVM_STATS_BASE_POW10`` + The scale is based on power of 10. It is used for measurement of time and + CPU clock cycles. + * ``KVM_STATS_BASE_POW2`` + The scale is based on power of 2. It is used for measurement of memory size. + +The ``exponent`` field is the scale of corresponding statistics data. For +example, if the unit is ``KVM_STATS_UNIT_BYTES``, the base is +``KVM_STATS_BASE_POW2``, the ``exponent`` is 10, then we know that the real +unit of the statistics data is KBytes a.k.a pow(2, 10) = 1024 bytes. +If the unit is ``KVM_STATS_UNIT_SECONDS``, the base is ``KVM_STATS_BASE_POW10``, +the ``exponent`` is -6, then we know that the real unit of the statistics data +is microsecond a.k.a 1 second * pow(10, -6) = 1 microsecond. + +The ``size`` field is the number of values of this statistics data. Its +value is usually 1 for most of simple statistics. 1 means it contains an +unsigned 64bit data. + +The ``offset`` field is the offset from the start of Data Block to the start of +the corresponding statistics data. + +The ``unused`` fields are reserved for future support for other types of +statistics data, like log/linear histogram. Its current value is always 0. + +The ``name`` field is the name string of the statistics data. The name string +starts at the end of ``struct kvm_stats_desc``. +The maximum length (including trailing '\0') is indicated by ``name_size`` +in ``struct kvm_stats_header``. + +The Stats Data block contains an array of statistics data whose type is __u64. +It would be read out by userspace periodically. +The order of data value in Stats Data block is the same as the order of +descriptors in Descriptors block. 5. The kvm_run structure ======================== @@ -6969,3 +7157,11 @@ The argument to KVM_ENABLE_CAP is also a bitmask, and must be a subset of the result of KVM_CHECK_EXTENSION. KVM will forward to userspace the hypercalls whose corresponding bit is in the argument, and return ENOSYS for the others. + +8.35 KVM_CAP_STATS_BINARY_FD +---------------------------- + +:Architectures: all + +This capability indicates the feature that userspace can create get a file +descriptor for every VM and VCPU to read statistics data in binary format.