Hi Fuad,
On Mon, Jun 14, 2021 at 2:57 AM Fuad Tabba tabba@google.com wrote:
Hi Jing,
On Thu, Jun 3, 2021 at 10:14 PM Jing Zhang jingzhangos@google.com wrote:
Update KVM API documentation for binary statistics.
Reviewed-by: David Matlack dmatlack@google.com Reviewed-by: Ricardo Koller ricarkol@google.com Signed-off-by: Jing Zhang jingzhangos@google.com
Documentation/virt/kvm/api.rst | 180 +++++++++++++++++++++++++++++++++ 1 file changed, 180 insertions(+)
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 7fcb2fd38f42..550bfbdf611b 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -5034,6 +5034,178 @@ 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_GET_STATS_FD +---------------------
nit: missing one - (to match the subtitle length)
+: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 for the lifetime of the file descriptor. +It is in the form of ``struct kvm_stats_header`` as below::
#define KVM_STATS_ID_MAXLEN 64struct 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 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_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_POW2struct 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.
filed -> field
- ``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:
Bits 8-11
- ``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];};
- The kvm_run structure
========================
@@ -6891,3 +7063,11 @@ 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.
nit: user space -> userspace (it's spelled that way throughout this document)
Cheers, /fuad
-- 2.32.0.rc1.229.g3e70b5a671-goog
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Thanks for the review! Jing