1PMLOOKUPDESC(3) Library Functions Manual PMLOOKUPDESC(3)
2
6 pmLookupDesc, pmReceiveDesc, pmRequestDesc - obtain a description for a
7 performance metric
8
10 #include <pcp/pmapi.h>
11 int pmLookupDesc(pmID pmid, pmDesc *desc)
13 int pmRequestDesc(int ctx, pmID pmid)
14 int pmReceiveDesc(int ctx, pmDesc *desc)
15 cc ... -lpcp
17
19 Given a Performance Metrics Identifier (PMID) as pmid, fill in the
20 given pmDesc structure, pointed to by the parameter desc, from the cur‐
21 rent Performance Metrics Application Programming Interface (PMAPI) con‐
22 text.
23 The pmDesc structure provides all of the information required to
25 describe and manipulate a performance metric via the PMAPI, and has the
26 following declaration.
27 /* Performance Metric Descriptor */
29 typedef struct {
30 pmID pmid; /* unique identifier */
31 int type; /* base data type (see below) */
32 pmInDom indom; /* instance domain */
33 int sem; /* semantics of value (see below) *
34 pmUnits units; /* dimension and units (see below) */
35 } pmDesc;
36 /* pmDesc.type -- data type of metric values */
38 #define PM_TYPE_NOSUPPORT -1 /* not impl. in this version */
39 #define PM_TYPE_32 0 /* 32-bit signed integer */
40 #define PM_TYPE_U32 1 /* 32-bit unsigned integer */
41 #define PM_TYPE_64 2 /* 64-bit signed integer */
42 #define PM_TYPE_U64 3 /* 64-bit unsigned integer */
43 #define PM_TYPE_FLOAT 4 /* 32-bit floating point */
44 #define PM_TYPE_DOUBLE 5 /* 64-bit floating point */
45 #define PM_TYPE_STRING 6 /* array of char */
46 #define PM_TYPE_AGGREGATE 7 /* arbitrary binary data */
47 #define PM_TYPE_AGGREGATE_STATIC 8 /* static pointer to aggregate */
48 #define PM_TYPE_UNKNOWN 255 /* used in pmValueBlock, not pmDesc */
49 /* pmDesc.sem -- semantics/interpretation of metric values */
52 #define PM_SEM_COUNTER 1 /* cumulative ctr (monotonic incr) */
53 #define PM_SEM_INSTANT 3 /* instant. value continuous domain */
54 #define PM_SEM_DISCRETE 4 /* instant. value discrete domain */
55 The type field in the pmDesc describes various encodings (or formats)
57 for a metric's value.
58 If a value is counted in the underlying base instrumentation with less
60 than 32 bits of integer precision, it is the responsibility of the Per‐
61 formance Metrics Domain Agent (PMDA) to promote the value to a 32-bit
62 integer before it is exported into the Performance Metrics Collection
63 Subsystem (PMCS); i.e. applications above the PMAPI never have to deal
64 with 8-bit and 16-bit counters.
65 If the value of a performance metric is of type PM_TYPE_AGGREGATE (or
67 indeed PM_TYPE_STRING), the interpretation of the value is unknown to
68 the PMCS. In these cases, the application using the value, and the
69 PMDA providing the value must have some common understanding about how
70 the value is structured and interpreted.
71 Each value for a performance metric is assumed to be drawn from a set
73 of values that can be described in terms of their dimensionality and
74 scale by a compact encoding as follows. The dimensionality is defined
75 by a power, or index, in each of 3 orthogonal dimensions, namely Space,
76 Time and Count (or Events, which are dimensionless). For example I/O
77 throughput might be represented as
78 -1
79 Space.Time
80 while the running total of system calls is Count, memory allocation is
81 Space and average service time is
82 -1
83 Time.Count
84 In each dimension there are a number of common scale values that may be
85 used to better encode ranges that might otherwise exhaust the precision
86 of a 32-bit value. This information is encoded in the pmUnits struc‐
87 ture which is embedded in the pmDesc structure.
88 /*
90 * Encoding for the units (dimensions Time and Space) and scale
91 * for Performance Metric Values
92 *
93 * For example, a pmUnits struct of
94 * { 1, -1, 0, PM_SPACE_MBYTE, PM_TIME_SEC, 0 }
95 * represents Mbytes/sec, while
96 * { 0, 1, -1, 0, PM_TIME_HOUR, 6 }
97 * represents hours/million-events
98 */
99 typedef struct {
100 int dimSpace:4; /* space dimension */
101 int dimTime:4; /* time dimension */
102 int dimCount:4; /* event dimension */
103 int scaleSpace:4; /* one of PM_SPACE_* below */
104 int scaleTime:4; /* one of PM_TIME_* below */
105 int scaleCount:4; /* one of PM_COUNT_* below */
106 } pmUnits; /* dimensional units and scale of value */
107 /* pmUnits.scaleSpace */
109 #define PM_SPACE_BYTE 0 /* bytes */
110 #define PM_SPACE_KBYTE 1 /* Kilobytes (1024) */
111 #define PM_SPACE_MBYTE 2 /* Megabytes (1024^2) */
112 #define PM_SPACE_GBYTE 3 /* Gigabytes (1024^3) */
113 #define PM_SPACE_TBYTE 4 /* Terabytes (1024^4) */
114 /* pmUnits.scaleTime */
115 #define PM_TIME_NSEC 0 /* nanoseconds */
116 #define PM_TIME_USEC 1 /* microseconds */
117 #define PM_TIME_MSEC 2 /* milliseconds */
118 #define PM_TIME_SEC 3 /* seconds */
119 #define PM_TIME_MIN 4 /* minutes */
120 #define PM_TIME_HOUR 5 /* hours */
121 /*
122 * pmUnits.scaleCount (e.g. count events, syscalls, interrupts,
123 * etc.) these are simply powers of 10, and not enumerated here,
124 * e.g. 6 for 10^6, or -3 for 10^-3
125 */
126 #define PM_COUNT_ONE 0 /* 1 */
127 Special routines (e.g. pmExtractValue(3), pmConvScale(3)) are provided
129 to manipulate values in conjunction with the pmUnits structure that
130 defines the dimension and scale of the values for a particular perfor‐
131 mance metric.
132 Below the PMAPI, the information required to complete the pmDesc struc‐
134 ture, is fetched from the PMDAs, and in this way the format and scale
135 of performance metrics may change dynamically, as the PMDAs and their
136 underlying instrumentation evolve with time. In particular, when some
137 metrics suddenly become 64-bits long, or change their units from Mbytes
138 to Gbytes, well-written applications using the services provided by the
139 PMAPI will continue to function correctly.
140 pmRequestDesc and pmReceiveDesc are used by applications which must
142 communicate with PMCD asynchronously. These functions take explict con‐
143 text handle ctx which must refer to a host context (i.e. a context cre‐
144 ated by passing PM_CONTEXT_HOST to pmNewContext). pmRequestDesc sends
145 request to PMCD and returns without waiting for the response, pmRe‐
146 ceiveDesc reads reply from PMCD. It is the responsibility of the appli‐
147 cation to make sure the data are ready before calling pmReceiveDesc to
148 avoid blocking.
149
151 PMAPI(3), pmAtomStr(3), pmConvScale(3), pmExtractValue(3), pmGetCon‐
152 fig(3), pmTypesStr(3), pmUnitsStr(3), pcp.conf(4) and pcp.env(4).
153
155 PM_ERR_PMID
156 The requested PMID is not known to the PMCS
157 PM_ERR_NOAGENT
159 The PMDA responsible for providing the metric is currently not
160 available
161 PM_ERR_CTXBUSY
163 Context is currently in use by another asynchronous call.
164Performance Co-Pilot SGI PMLOOKUPDESC(3)