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KVM: stats: Update doc for histogram statistics

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Add documentations for linear and logarithmic histogram statistics.

Signed-off-by: Jing Zhang <jingzhangos@google.com>
Message-Id: <20210802165633.1866976-3-jingzhangos@google.com>
[Small changes to the phrasing. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Jing Zhang 2021-08-02 16:56:30 +00:00 • committed by Paolo Bonzini
parent f95937ccf5
commit 0176ec5129
1 changed files with 27 additions and 8 deletions
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35
Documentation/virt/kvm/api.rst
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@ -5207,6 +5207,9 @@ by a string of size ``name_size``.
#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_LINEAR_HIST (0x3 << KVM_STATS_TYPE_SHIFT)
#define KVM_STATS_TYPE_LOG_HIST (0x4 << KVM_STATS_TYPE_SHIFT)
#define KVM_STATS_TYPE_MAX KVM_STATS_TYPE_LOG_HIST
#define KVM_STATS_UNIT_SHIFT 4
#define KVM_STATS_UNIT_MASK (0xF << KVM_STATS_UNIT_SHIFT)
@ -5214,18 +5217,20 @@ by a string of size ``name_size``.
#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;
__u32 bucket_size;
char name[];
};
@ -5235,21 +5240,35 @@ 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.
The statistics reports a cumulative count. 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
The statistics reports an instantaneous value. 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. The value of data can only be increased, and
represents a peak value for a measurement, for example the maximum number
The statistics data reports a peak value, for example the maximum number
of items in a hash table bucket, the longest time waited and so on.
The value of data can only be increased.
The corresponding ``size`` field for this type is always 1.
* ``KVM_STATS_TYPE_LINEAR_HIST``
The statistic is reported as a linear histogram. The number of
buckets is specified by the ``size`` field. The size of buckets is specified
by the ``hist_param`` field. The range of the Nth bucket (1 <= N < ``size``)
is [``hist_param``*(N-1), ``hist_param``*N), while the range of the last
bucket is [``hist_param``*(``size``-1), +INF). (+INF means positive infinity
value.) The bucket value indicates how many samples fell in the bucket's range.
* ``KVM_STATS_TYPE_LOG_HIST``
The statistic is reported as a logarithmic histogram. The number of
buckets is specified by the ``size`` field. The range of the first bucket is
[0, 1), while the range of the last bucket is [pow(2, ``size``-2), +INF).
Otherwise, The Nth bucket (1 < N < ``size``) covers
[pow(2, N-2), pow(2, N-1)). The bucket value indicates how many samples fell
in the bucket's range.
Bits 4-7 of ``flags`` encode the unit:
* ``KVM_STATS_UNIT_NONE``
@ -5282,9 +5301,9 @@ 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`` field is reserved for future support for other types of
statistics data, like log/linear histogram. Its value is always 0 for the types
defined above.
The ``bucket_size`` field is used as a parameter for histogram statistics data.
It is only used by linear histogram statistics data, specifying the size of a
bucket.
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