On Mon, May 24, 2021 at 8:18 AM Jing Zhang <jingzhangos@xxxxxxxxxx> wrote:
>
> Update KVM API documentation for binary statistics.
>
> Reviewed-by: David Matlack <dmatlack@xxxxxxxxxx>
> Reviewed-by: Ricardo Koller <ricarkol@xxxxxxxxxx>
> Signed-off-by: Jing Zhang <jingzhangos@xxxxxxxxxx>
Reviewed-by: David Matlack <dmatlack@xxxxxxxxxx>
> ---
> Documentation/virt/kvm/api.rst | 179 +++++++++++++++++++++++++++++++++
> 1 file changed, 179 insertions(+)
>
> diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
> index 7fcb2fd38f42..5cedddd579b2 100644
> --- a/Documentation/virt/kvm/api.rst
> +++ b/Documentation/virt/kvm/api.rst
> @@ -5034,6 +5034,177 @@ 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.
>
> +4.130 KVM_STATS_GETFD
> +---------------------
> +
> +: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. The file data is organized into three blocks as below:
> ++-------------+
> +| Header |
> ++-------------+
> +| Descriptors |
> ++-------------+
> +| Stats Data |
> ++-------------+
> +
> +The Header block is always at the start of the file. It is only needed to be
> +read one time after a VM boot.
nit: "after a VM boot" is not exactly right. If a VM reboots,
userspace does not need to re-read the header. Perhaps change this to
"for the lifetime of the file descriptor"?
> +It is in the form of ``struct kvm_stats_header`` as below::
> +
> + #define KVM_STATS_ID_MAXLEN 64
> +
> + struct kvm_stats_header {
> + char id[KVM_STATS_ID_MAXLEN];
> + __u32 name_size;
> + __u32 count;
> + __u32 desc_offset;
> + __u32 data_offset;
> + };
> +
> +The ``id`` field is identification for 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 ``name_size`` field is the size (byte) of the statistics name string
> +(including trailing '\0') appended to the end of every statistics descriptor.
> +
> +The ``count`` field is the number of statistics.
> +
> +The ``desc_offset`` field is the offset of the Descriptors block from the start
> +of the file indicated by the file descriptor.
> +
> +The ``data_offset`` field is the offset of the Stats Data block from the start
> +of the file indicated by the file descriptor.
> +
> +The Descriptors block is only needed to be read once after a VM boot. It is
Ditto here.
> +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_MAX KVM_STATS_TYPE_INSTANT
> +
> + #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 unused1;
> + __u32 unused2;
> + char name[0];
> + };
> +
> +The ``flags`` field contains the type and unit of the statistics data described
> +by this descriptor. 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 ``count`` filed for this type is always 1.
> + * ``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.
> + The corresponding ``count`` 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 7-11 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.
> +
> +The ``size`` field is the number of values of this statistics data. It is in the
> +unit of ``unsigned long`` for VM or ``__u64`` for VCPU.
> +
> +The ``unused1`` and ``unused2`` fields are reserved for future
> +support for other types of statistics data, like log/linear histogram.
> +
> +The ``name`` field points to 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 data values of type ``struct
> +kvm_vm_stats_data`` or ``struct kvm_vcpu_stats_data``. It would be read by
> +user space periodically to pull statistics data.
> +The order of data value in Stats Data block is the same as the order of
> +descriptors in Descriptors block.
> + * Statistics data for VM::
> +
> + struct kvm_vm_stats_data {
> + unsigned long value[0];
> + };
> +
> + * Statistics data for VCPU::
> +
> + struct kvm_vcpu_stats_data {
> + __u64 value[0];
> + };
> +
> 5. The kvm_run structure
> ========================
>
> @@ -6891,3 +7062,11 @@ This capability is always enabled.
> This capability indicates that the KVM virtual PTP service is
> supported in the host. A VMM can check whether the service is
> available to the guest on migration.
> +
> +8.33 KVM_CAP_STATS_BINARY_FD
> +----------------------------
> +
> +:Architectures: all
> +
> +This capability indicates the feature that user space can create get a file
> +descriptor for every VM and VCPU to read statistics data in binary format.
> --
> 2.31.1.818.g46aad6cb9e-goog
>
