STATS(3) FreeBSD Library Functions Manual STATS(3)
NAME
stats - statistics gathering
LIBRARY
library "libstats"
SYNOPSIS
#include <sys/arb.h>
#include <sys/qmath.h>
#include <sys/stats.h>
Stats Blob Template Management Functions
int
stats_tpl_alloc(const char *name, uint32_t flags);
int
stats_tpl_fetch_allocid(const char *name, uint32_t hash);
int
stats_tpl_fetch(int tpl_id, struct statsblob_tpl **tpl);
int
stats_tpl_id2name(uint32_t tpl_id, char *buf, size_t len);
int
stats_tpl_sample_rates(SYSCTL_HANDLER_ARGS);
int
stats_tpl_sample_rollthedice(struct stats_tpl_sample_rate *rates,
int nrates, void *seed_bytes, size_t seed_len);
struct voistatspec
STATS_VSS_SUM();
struct voistatspec
STATS_VSS_MAX();
struct voistatspec
STATS_VSS_MIN();
struct voistatspec
STATS_VSS_CRHIST<32|64>_LIN(lb, ub, stepinc, vsdflags);
struct voistatspec
STATS_VSS_CRHIST<32|64>_EXP(lb, ub, stepbase, stepexp, vsdflags);
struct voistatspec
STATS_VSS_CRHIST<32|64>_LINEXP(lb, ub, nlinsteps, stepbase, vsdflags);
struct voistatspec
STATS_VSS_CRHIST<32|64>_USR(HBKTS(CRBKT(lb), ...), vsdflags);
struct voistatspec
STATS_VSS_DRHIST<32|64>_USR(HBKTS(DRBKT(lb, ub), ...), vsdflags);
struct voistatspec
STATS_VSS_DVHIST<32|64>_USR(HBKTS(DVBKT(val), ...), vsdflags);
struct voistatspec
STATS_VSS_TDGSTCLUST<32|64>(nctroids, prec);
int
stats_tpl_add_voistats(uint32_t tpl_id, int32_t voi_id,
const char *voi_name, enum vsd_dtype voi_dtype, uint32_t nvss,
struct voistatspec *vss, uint32_t flags);
Stats Blob Data Gathering Functions
int
stats_voi_update_<abs|rel>_<dtype>(struct statsblob *sb, int32_t voi_id,
<dtype> voival);
Stats Blob Utility Functions
struct statsblob *
stats_blob_alloc(uint32_t tpl_id, uint32_t flags);
int
stats_blob_init(struct statsblob *sb, uint32_t tpl_id, uint32_t flags);
int
stats_blob_clone(struct statsblob **dst, size_t dstmaxsz,
struct statsblob *src, uint32_t flags);
void
stats_blob_destroy(struct statsblob *sb);
int
stats_voistat_fetch_dptr(struct statsblob *sb, int32_t voi_id,
enum voi_stype stype, enum vsd_dtype *retdtype,
struct voistatdata **retvsd, size_t *retvsdsz);
int
stats_voistat_fetch_<dtype>(struct statsblob *sb, int32_t voi_id,
enum voi_stype stype, <dtype> *ret);
int
stats_blob_snapshot(struct statsblob **dst, size_t dstmaxsz,
struct statsblob *src, uint32_t flags);
int
stats_blob_tostr(struct statsblob *sb, struct sbuf *buf,
enum sb_str_fmt fmt, uint32_t flags);
int
stats_voistatdata_tostr(const struct voistatdata *vsd,
enum vsd_dtype dtype, enum sb_str_fmt fmt, struct sbuf *buf,
int objdump);
typedef int
(*stats_blob_visitcb_t)(struct sb_visit *sbv, void *usrctx);)(struct sb_visit *sbv, void *usrctx);
int
stats_blob_visit(struct statsblob *sb, stats_blob_visitcb_t func,
void *usrctx);
DESCRIPTION
The stats framework facilitates real-time kernel and user space
statistics gathering. The framework is built around the "statsblob", an
object embedded within a contiguous memory allocation that is mostly
opaque to consumers and stores all required state. A "statsblob" object
can itself be embedded within other objects either directly or indirectly
using a pointer.
Objects or subsystems for which statistics are to be gathered are
initialized from a template "statsblob", which acts as the blueprint for
an arbitrary set of Variables Of Interest (VOIs) and their associated
statistics. Each template defines a schema plus associated metadata,
which are kept separate to minimize the memory footprint of blobs.
Data gathering hook functions added at appropriate locations within the
code base of interest feed VOI data into the framework for processing.
Each "statsblob", consists of a struct statsblob header and opaque
internal blob structure per the following diagram:
---------------------------------------------------------
| struct | uint8_t |
| statsblob | opaque[] |
---------------------------------------------------------
The publicly visible 8-byte header is defined as:
struct statsblob {
uint8_t abi;
uint8_t endian;
uint16_t flags;
uint16_t maxsz;
uint16_t cursz;
uint8_t opaque[];
};
abi specifies which API version the blob's opaque internals conform to
(STATS_ABI_V1 is the only version currently defined). endian specifies
the endianness of the blob's fields (SB_LE for little endian, SB_BE for
big endian, or SB_UE for unknown endianness). cursz specifies the size
of the blob, while maxsz specifies the size of the underlying memory
allocation in which the blob is embedded. Both cursz and maxsz default
to units of bytes, unless a flag is set in flags that dictates otherwise.
Templates are constructed by associating arbitrary VOI IDs with a set of
statistics, where each statistic is specified using a struct voistatspec
per the definition below:
struct voistatspec {
vss_hlpr_fn hlpr;
struct vss_hlpr_info *hlprinfo;
struct voistatdata *iv;
size_t vsdsz;
uint32_t flags;
enum vsd_dtype vs_dtype : 8;
enum voi_stype stype : 8;
};
It is generally expected that consumers will not work with struct
voistatspec directly, and instead use the STATS_VSS_*() helper macros.
The stats framework offers the following statistics for association with
VOIs:
VS_STYPE_SUM The sum of VOI values.
VS_STYPE_MAX The maximum VOI value.
VS_STYPE_MIN The minimum VOI value.
VS_STYPE_HIST A static bucket histogram of VOI values, including a
count of "out-of-band/bucket" values which did not
match any bucket. Histograms can be specified as
"Continuous Range" (CRHIST), "Discrete Range"
(DRHIST) or "Discrete Value" (DVHIST), with 32 or 64
bit bucket counters, depending on the VOI semantics.
VS_STYPE_TDGST A dynamic bucket histogram of VOI values based on the
t-digest method (refer to the t-digest paper in the
SEE ALSO section below).
A "visitor software design pattern"-like scheme is employed to facilitate
iterating over a blob's data without concern for the blob's structure.
The data provided to visitor callback functions is encapsulated in struct
sb_visit per the definition below:
struct sb_visit {
struct voistatdata *vs_data;
uint32_t tplhash;
uint32_t flags;
int16_t voi_id;
int16_t vs_dsz;
enum vsd_dtype voi_dtype : 8;
enum vsd_dtype vs_dtype : 8;
int8_t vs_stype;
uint16_t vs_errs;
};
The stats_tpl_sample_rates() and stats_tpl_sample_rollthedice() functions
utilize struct stats_tpl_sample_rate to encapsulate per-template sample
rate information per the definition below:
struct stats_tpl_sample_rate {
int32_t tpl_slot_id;
uint32_t tpl_sample_pct;
};
The tpl_slot_id member holds the template's slot ID obtained from
stats_tpl_alloc() or stats_tpl_fetch_allocid(). The tpl_sample_pct
member holds the template's sample rate as an integer percentage in the
range [0,100].
The stats_tpl_sr_cb_t conformant function pointer that is required as the
arg1 of stats_tpl_sample_rates() is defined as:
enum stats_tpl_sr_cb_action {
TPL_SR_UNLOCKED_GET,
TPL_SR_RLOCKED_GET,
TPL_SR_RUNLOCK,
TPL_SR_PUT
};
typedef int (*stats_tpl_sr_cb_t)(enum stats_tpl_sr_cb_action action,
struct stats_tpl_sample_rate **rates, int *nrates, void *ctx);
It is required that a conformant function:
- Return an appropriate errno(2) on error, otherwise 0.
- When called with "action == TPL_SR_*_GET", return the subsystem's
rates list ptr and count, locked or unlocked as requested.
- When called with "action == TPL_SR_RUNLOCK", unlock the subsystem's
rates list ptr and count. Pair with a prior "action ==
TPL_SR_RLOCKED_GET" call.
- When called with "action == TPL_SR_PUT", update the subsystem's rates
list ptr and count to the sysctl processed values and return the
inactive list details in rates and nrates for garbage collection by
stats_tpl_sample_rates().
Where templates need to be referenced via textual means, for example via
a MIB variable, the following string based template spec formats can be
used:
1. "<tplname>":<tplhash>, for example "TCP_DEFAULT":1731235399
2. "<tplname>", for example "TCP_DEFAULT"
3. :<tplhash>, for example :1731235399
The first form is the normative spec format generated by the framework,
while the second and third forms are convenience formats primarily for
user input. The use of inverted commas around the template name is
optional.
MIB Variables
The in-kernel stats framework exposes the following framework-specific
variables in the kern.stats branch of the sysctl(3) MIB.
templates Read-only CSV list of registered templates in normative
template spec form.
Template Management Functions
The stats_tpl_alloc() function allocates a new template with the
specified unique name and returns its runtime-stable template slot ID for
use with other API functions. The flags argument is currently unused.
The stats_tpl_fetch_allocid() function returns the runtime-stable
template slot ID of any registered template matching the specified name
and hash.
The stats_tpl_fetch() function returns the pointer to the registered
template object at the specified template slot ID.
The stats_tpl_id2name() function returns the name of the registered
template object at the specified template slot ID.
The stats_tpl_sample_rates() function provides a generic handler for
template sample rates management and reporting via sysctl(3) MIB
variables. Subsystems can use this function to create a subsystem-
specific SYSCTL_PROC(9) MIB variable that manages and reports subsystem-
specific template sampling rates. Subsystems must supply a
stats_tpl_sr_cb_t conformant function pointer as the sysctl's arg1, which
is a callback used to interact with the subsystem's stats template sample
rates list. Subsystems can optionally specify the sysctl's arg2 as non-
zero, which causes a zero-initialized allocation of arg2-sized contextual
memory to be heap-allocated and passed in to all subsystem callbacks made
during the operation of stats_tpl_sample_rates().
The stats_tpl_sample_rollthedice() function makes a weighted random
template selection from the supplied array of template sampling rates.
The cumulative percentage of all sampling rates should not exceed 100.
If no seed is supplied, a PRNG is used to generate a true random number
so that every selection is independent. If a seed is supplied, selection
will be made randomly across different seeds, but deterministically given
the same seed.
The stats_tpl_add_voistats() function is used to add a VOI and associated
set of statistics to the registered template object at the specified
template slot ID. The set of statistics is passed as an array of struct
voistatspec which can be initialized using the STATS_VSS_*() helper
macros or manually for non-standard use cases. For static vss arrays,
the nvss count of array elements can be determined by passing vss to the
NVSS() macro. The SB_VOI_RELUPDATE flag can be passed to configure the
VOI for use with stats_voi_update_rel_<dtype>(), which entails
maintaining an extra 8 bytes of state in the blob at each update.
Data Gathering Functions
The stats_voi_update_abs_<dtype>() and stats_voi_update_rel_<dtype>()
functions both update all the statistics associated with the VOI
identified by voi_id. The "abs" call uses voival as an absolute value,
whereas the "rel" call uses voival as a value relative to that of the
previous update function call, by adding it to the previous value and
using the result for the update. Relative updates are only possible for
VOIs that were added to the template with the SB_VOI_RELUPDATE flag
specified to stats_tpl_add_voistats().
Utility Functions
The stats_blob_alloc() function allocates and initializes a new blob
based on the registered template object at the specified template slot
ID.
The stats_blob_init() function initializes a new blob in an existing
memory allocation based on the registered template object at the
specified template slot ID.
The stats_blob_clone() function duplicates the src blob into dst, leaving
only the maxsz field of dst untouched. The SB_CLONE_ALLOCDST flag can be
passed to instruct the function to allocate a new blob of appropriate
size into which to clone src, storing the new pointer in *dst. The
SB_CLONE_USRDSTNOFAULT or SB_CLONE_USRDST flags can be set to
respectively signal that copyout_nofault(9) or copyout(9) should be used
because *dst is a user space address.
The stats_blob_snapshot() function calls stats_blob_clone() to obtain a
copy of src and then performs any additional functions required to
produce a coherent blob snapshot. The flags interpreted by
stats_blob_clone() also apply to stats_blob_snapshot(). Additionally,
the SB_CLONE_RSTSRC flag can be used to effect a reset of the src blob's
statistics after a snapshot is successfully taken.
The stats_blob_destroy() function destroys a blob previously created with
stats_blob_alloc(), stats_blob_clone() or stats_blob_snapshot().
The stats_blob_visit() function allows the caller to iterate over the
contents of a blob. The callback function func is called for every VOI
and statistic in the blob, passing a struct sb_visit and the user context
argument usrctx to the callback function. The sbv passed to the callback
function may have one or more of the following flags set in the flags
struct member to provide useful metadata about the iteration:
SB_IT_FIRST_CB, SB_IT_LAST_CB, SB_IT_FIRST_VOI, SB_IT_LAST_VOI,
SB_IT_FIRST_VOISTAT, SB_IT_LAST_VOISTAT, SB_IT_NULLVOI and
SB_IT_NULLVOISTAT. Returning a non-zero value from the callback function
terminates the iteration.
The stats_blob_tostr() renders a string representation of a blob into the
sbuf(9) buf. Currently supported render formats are SB_STRFMT_FREEFORM
and SB_STRFMT_JSON. The SB_TOSTR_OBJDUMP flag can be passed to render
version specific opaque implementation detail for debugging or string-to-
binary blob reconstruction purposes. The SB_TOSTR_META flag can be
passed to render template metadata into the string representation, using
the blob's template hash to lookup the corresponding template.
The stats_voistatdata_tostr() renders a string representation of an
individual statistic's data into the sbuf(9) buf. The same render
formats supported by the stats_blob_tostr() function can be specified,
and the objdump boolean has the same meaning as the SB_TOSTR_OBJDUMP
flag.
The stats_voistat_fetch_dptr() function returns an internal blob pointer
to the specified stype statistic data for the VOI voi_id. The
stats_voistat_fetch_<dtype>() functions are convenience wrappers around
stats_voistat_fetch_dptr() to perform the extraction for simple data
types.
IMPLEMENTATION NOTES
The following notes apply to STATS_ABI_V1 format statsblobs.
Space-Time Complexity
Blobs are laid out as three distinct memory regions following the header:
------------------------------------------------------
| struct | struct | struct | struct |
| statsblobv1 | voi [] | voistat [] | voistatdata [] |
------------------------------------------------------
Blobs store VOI and statistic blob state (8 bytes for struct voi and 8
bytes for struct voistat respectively) in sparse arrays, using the voi_id
and enum voi_stype as array indices. This allows O(1) access to any
voi/voistat pair in the blob, at the expense of 8 bytes of wasted memory
per vacant slot for templates which do not specify contiguously numbered
VOIs and/or statistic types. Data storage for statistics is only
allocated for non-vacant slot pairs.
To provide a concrete example, a blob with the following specification:
- Two VOIs; ID 0 and 2; added to the template in that order
- VOI 0 is of data type int64_t, is configured with SB_VOI_RELUPDATE to
enable support for relative updates using
stats_voi_update_rel_<dtype>(), and has a VS_STYPE_MIN statistic
associated with it.
- VOI 2 is of data type uint32_t with VS_STYPE_SUM and VS_STYPE_MAX
statistics associated with it.
would have the following memory layout:
--------------------------------------
| header | struct statsblobv1, 32 bytes
|------------------------------------|
| voi[0] | struct voi, 8 bytes
| voi[1] (vacant) | struct voi, 8 bytes
| voi[2] | struct voi, 8 bytes
|------------------------------------|
| voi[2]voistat[VOISTATE] (vacant) | struct voistat, 8 bytes
| voi[2]voistat[SUM] | struct voistat, 8 bytes
| voi[2]voistat[MAX] | struct voistat, 8 bytes
| voi[0]voistat[VOISTATE] | struct voistat, 8 bytes
| voi[0]voistat[SUM] (vacant) | struct voistat, 8 bytes
| voi[0]voistat[MAX] (vacant) | struct voistat, 8 bytes
| voi[0]voistat[MIN] | struct voistat, 8 bytes
|------------------------------------|
| voi[2]voistat[SUM]voistatdata | struct voistatdata_int32, 4 bytes
| voi[2]voistat[MAX]voistatdata | struct voistatdata_int32, 4 bytes
| voi[0]voistat[VOISTATE]voistatdata | struct voistatdata_numeric, 8 bytes
| voi[0]voistat[MIN]voistatdata | struct voistatdata_int64, 8 bytes
--------------------------------------
TOTAL 136 bytes
When rendered to string format using stats_blob_tostr(), the
SB_STRFMT_FREEFORM fmt and the SB_TOSTR_OBJDUMP flag, the rendered output
is:
struct statsblobv1@0x8016250a0, abi=1, endian=1, maxsz=136, cursz=136, \
created=6294158585626144, lastrst=6294158585626144, flags=0x0000, \
stats_off=56, statsdata_off=112, tplhash=2994056564
vois[0]: id=0, name="", flags=0x0001, dtype=INT_S64, voistatmaxid=3, \
stats_off=80
vois[0]stat[0]: stype=VOISTATE, flags=0x0000, dtype=VOISTATE, \
dsz=8, data_off=120
voistatdata: prev=0
vois[0]stat[1]: stype=-1
vois[0]stat[2]: stype=-1
vois[0]stat[3]: stype=MIN, flags=0x0000, dtype=INT_S64, \
dsz=8, data_off=128
voistatdata: 9223372036854775807
vois[1]: id=-1
vois[2]: id=2, name="", flags=0x0000, dtype=INT_U32, voistatmaxid=2, \
stats_off=56
vois[2]stat[0]: stype=-1
vois[2]stat[1]: stype=SUM, flags=0x0000, dtype=INT_U32, dsz=4, \
data_off=112
voistatdata: 0
vois[2]stat[2]: stype=MAX, flags=0x0000, dtype=INT_U32, dsz=4, \
data_off=116
voistatdata: 0
Note: The "\" present in the rendered output above indicates a manual
line break inserted to keep the man page within 80 columns and is not
part of the actual output.
Locking
The stats framework does not provide any concurrency protection at the
individual blob level, instead requiring that consumers guarantee mutual
exclusion when calling API functions that reference a non-template blob.
The list of templates is protected with a rwlock(9) in-kernel, and
pthread(3) rw lock in user space to support concurrency between template
management and blob initialization operations.
RETURN VALUES
stats_tpl_alloc() returns a runtime-stable template slot ID on success,
or a negative errno on failure. -EINVAL is returned if any problems are
detected with the arguments. -EEXIST is returned if an existing template
is registered with the same name. -ENOMEM is returned if a required
memory allocation fails.
stats_tpl_fetch_allocid() returns a runtime-stable template slot ID, or
negative errno on failure. -ESRCH is returned if no registered template
matches the specified name and/or hash.
stats_tpl_fetch() returns 0 on success, or ENOENT if an invalid tpl_id is
specified.
stats_tpl_id2name() returns 0 on success, or an errno on failure.
EOVERFLOW is returned if the length of buf specified by len is too short
to hold the template's name. ENOENT is returned if an invalid tpl_id is
specified.
stats_tpl_sample_rollthedice() returns a valid template slot id selected
from rates or -1 if a NULL selection was made, that is no stats
collection this roll.
stats_tpl_add_voistats() return 0 on success, or an errno on failure.
EINVAL is returned if any problems are detected with the arguments.
EFBIG is returned if the resulting blob would have exceeded the maximum
size. EOPNOTSUPP is returned if an attempt is made to add more VOI stats
to a previously configured VOI. ENOMEM is returned if a required memory
allocation fails.
stats_voi_update_abs_<dtype>() and stats_voi_update_rel_<dtype>() return
0 on success, or EINVAL if any problems are detected with the arguments.
stats_blob_init() returns 0 on success, or an errno on failure. EINVAL
is returned if any problems are detected with the arguments. EOVERFLOW
is returned if the template blob's cursz is larger than the maxsz of the
blob being initialized.
stats_blob_alloc() returns a pointer to a newly allocated and initialized
blob based on the specified template with slot ID tpl_id, or NULL if the
memory allocation failed.
stats_blob_clone() and stats_blob_snapshot() return 0 on success, or an
errno on failure. EINVAL is returned if any problems are detected with
the arguments. ENOMEM is returned if the SB_CLONE_ALLOCDST flag was
specified and the memory allocation for dst fails. EOVERFLOW is returned
if the src blob's cursz is larger than the maxsz of the dst blob.
stats_blob_visit() returns 0 on success, or EINVAL if any problems are
detected with the arguments.
stats_blob_tostr() and stats_voistatdata_tostr() return 0 on success, or
an errno on failure. EINVAL is returned if any problems are detected
with the arguments, otherwise any error returned by sbuf_error() for buf
is returned.
stats_voistat_fetch_dptr() returns 0 on success, or EINVAL if any
problems are detected with the arguments.
stats_voistat_fetch_<dtype>() returns 0 on success, or an errno on
failure. EINVAL is returned if any problems are detected with the
arguments. EFTYPE is returned if the requested data type does not match
the blob's data type for the specified voi_id and stype.
SEE ALSO
errno(2), arb(3), qmath(3), tcp(4), sbuf(9)
Ted Dunning and Otmar Ertl, Computing Extremely Accurate Quantiles Using
t-digests,
https://github.com/tdunning/t-digest/raw/master/docs/t-digest-paper/histo.pdf.
HISTORY
The stats framework first appeared in FreeBSD 13.0.
AUTHORS
The stats framework and this manual page were written by Lawrence Stewart
<lstewart@FreeBSD.org> and sponsored by Netflix, Inc.
CAVEATS
Granularity of timing-dependent network statistics, in particular
TCP_RTT, depends on the HZ timer. To minimize the measurement error
avoid using HZ lower than 1000.
FreeBSD 13.1-RELEASE-p6 December 2, 2019 FreeBSD 13.1-RELEASE-p6
man2web Home...