Commit 0176ec51 authored by Jing Zhang's avatar Jing Zhang Committed by Paolo Bonzini
Browse files

KVM: stats: Update doc for histogram statistics 



Add documentations for linear and logarithmic histogram statistics.

Signed-off-by: default avatarJing Zhang <jingzhangos@google.com>
Message-Id: <20210802165633.1866976-3-jingzhangos@google.com>
[Small changes to the phrasing. - Paolo]
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent f95937cc

Documentation/virt/kvm/api.rst

+27 −8
Original line number Diff line number Diff line
@@ -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