From 0176ec51290f8ef543a8c18a02e932d6ccedbbc5 Mon Sep 17 00:00:00 2001 From: Jing Zhang Date: Mon, 2 Aug 2021 16:56:30 +0000 Subject: KVM: stats: Update doc for histogram statistics Add documentations for linear and logarithmic histogram statistics. Signed-off-by: Jing Zhang Message-Id: <20210802165633.1866976-3-jingzhangos@google.com> [Small changes to the phrasing. - Paolo] Signed-off-by: Paolo Bonzini --- Documentation/virt/kvm/api.rst | 35 +++++++++++++++++++++++++++-------- 1 file changed, 27 insertions(+), 8 deletions(-) (limited to 'Documentation/virt') diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index dae68e68ca23..86d7ad3a126c 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -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 -- cgit v1.2.3