1PMDA(3) Library Functions Manual PMDA(3)
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6 PMDA - introduction to the Performance Metrics Domain Agent support
7 library
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10 #include <pcp/pmapi.h>
11 #include <pcp/pmda.h>
12 cc ... -lpcp_pmda -lpcp
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16 To assist in the development of Performance Metric Domain Agents
17 (PMDAs) for the Performance Co-Pilot (PCP), a procedural interface is
18 provided that extends the Performance Metrics Application Programming
19 Interface ( PMAPI(3)) library. These procedures are designed to enable
20 a programmer to quickly build a PMDA which can then be tested and
21 refined. However, this also implies that a PMDA has a particular
22 structure which may not be suitable for all PMDA implementations.
23 Once you are familiar with the PCP and PMDA frameworks, you can quickly
25 implement a new PMDA with only a few data structures and functions.
26 This is covered in far greater detail in the Performance Co-Pilot Pro‐
27 grammer's Guide.
28 A PMDA is responsible for a set of performance metrics, in the sense
30 that it must respond to requests from pmcd(1) for information about
31 performance metrics, instance domains, and instantiated values.
32 This man page contains sections of the simple PMDA which is located at
34 $PCP_PMDAS_DIR/simple.
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37 Two approaches may be used for connecting a PMDA to a pmcd(1) process.
38 A Dynamic Shared Object (DSO) can be attached by pmcd(1) using
39 dlopen(3) when the pmcd(1) process is started. A procedural interface
40 referenced through a shared data structure is used to handle requests
41 from pmcd(1) to the PMDA .
42 The preferred approach is for a separate process (daemon) to communi‐
44 cate with pmcd(1) using the Performance Data Units (PDU) Inter-Process
45 Communication (IPC) protocol.
46 All PMDAs are launched and controlled by the pmcd(1) process on the
48 local host. The requests from the clients are received by pmcd(1) and
49 forwarded to the appropriate PMDAs. Responses, when required, are
50 returned through pmcd(1) to the clients. The requests (PDUs) that may
51 be sent to a PMDA from pmcd(1) are PDU_FETCH, PDU_PROFILE,
52 PDU_INSTANCE_REQ, PDU_DESC_REQ, PDU_TEXT_REQ and PDU_RESULT. If the
53 PMDA implements any dynamic metrics it may also receive PDU_PMNS_CHILD,
54 PDU_PMNS_IDS, PDU_PMNS_NAMES and PDU_PMNS_TRAVERSE PDUs.
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57 To allow a consistent framework, pmdaMain(3) can be used by a daemon
58 PMDA to handle the communication protocol using the same ca