4. Monitoring System Performance

This chapter describes the performance monitoring tools available in Performance Co-Pilot (PCP). This product provides a group of commands and tools for measuring system performance. Each tool is described completely by its own man page. The man pages are accessible through the man command. For example, the man page for the tool pmrep is viewed by entering the following command:

man pmrep

The following major sections are covered in this chapter:

Section 4.1, “The pmstat Command”, discusses pmstat, a utility that provides a periodic one-line summary of system performance.

Section 4.2, “The pmrep Command”, discusses pmrep, a utility that shows the current values for named performance metrics.

Section 4.3, “The pmval Command”, describes pmval, a utility that displays performance metrics in a textual format.

Section 4.4, “The pminfo Command”, describes pminfo, a utility that displays information about performance metrics.

Section 4.5, “The pmstore Command”, describes the use of the pmstore utility to arbitrarily set or reset selected performance metric values.

The following sections describe the various graphical and text-based PCP tools used to monitor local or remote system performance.

4.1. The pmstat Command

The pmstat command provides a periodic, one-line summary of system performance. This command is intended to monitor system performance at the highest level, after which other tools may be used for examining subsystems to observe potential performance problems in greater detail. After entering the pmstat command, you see output similar to the following, with successive lines appearing periodically:

pmstat
@ Thu Aug 15 09:25:56 2017
 loadavg                      memory      swap        io    system         cpu
   1 min   swpd   free   buff  cache   pi   po   bi   bo   in   cs  us  sy  id
    1.29 833960  5614m 144744 265824    0    0    0 1664  13K  23K   6   7  81
    1.51 833956  5607m 144744 265712    0    0    0 1664  13K  24K   5   7  83
    1.55 833956  5595m 145196 271908    0    0  14K 1056  13K  24K   7   7  74

An additional line of output is added every five seconds. The -t interval option may be used to vary the update interval (i.e. the sampling interval).

The output from pmstat is directed to standard output, and the columns in the report are interpreted as follows:

loadavg

The 1-minute load average (runnable processes).

memory

The swpd column indicates average swap space used during the interval (all columns reported in Kbytes unless otherwise indicated). The free column indicates average free memory during the interval. The buff column indicates average buffer memory in use during the interval. The cache column indicates average cached memory in use during the interval.

swap

Reports the average number of pages that are paged-in (pi) and paged-out (po) per second during the interval. It is normal for the paged-in values to be non-zero, but the system is suffering memory stress if the paged-out values are non-zero over an extended period.

io

The bi and bo columns indicate the average rate per second of block input and block output operations respectfully, during the interval. These rates are independent of the I/O block size. If the values become large, they are reported as thousands of operations per second (K suffix) or millions of operations per second (M suffix).

system

Context switch rate (cs) and interrupt rate (in). Rates are expressed as average operations per second during the interval. Note that the interrupt rate is normally at least HZ (the clock interrupt rate, and kernel.all.hz metric) interrupts per second.

cpu

Percentage of CPU time spent executing user code (us), system and interrupt code (sy), idle loop (id).

As with most PCP utilities, real-time metric, and archives are interchangeable.

For example, the following command uses a local system PCP archive 20170731 and the timezone of the host (smash) from which performance metrics in the archive were collected:

pmstat -a ${PCP_LOG_DIR}/pmlogger/smash/20170731 -t 2hour -A 1hour -z
Note: timezone set to local timezone of host "smash"
@ Wed Jul 31 10:00:00 2017
 loadavg                      memory      swap        io    system         cpu
   1 min   swpd   free   buff  cache   pi   po   bi   bo   in   cs  us  sy  id
    3.90  24648  6234m 239176  2913m    ?    ?    ?    ?    ?    ?   ?   ?   ?
    1.72  24648  5273m 239320  2921m    0    0    4   86  11K  19K   5   5  84
    3.12  24648  5194m 241428  2969m    0    0    0   84  10K  19K   5   5  85
    1.97  24644  4945m 244004  3146m    0    0    0   84  10K  19K   5   5  84
    3.82  24640  4908m 244116  3147m    0    0    0   83  10K  18K   5   5  85
    3.38  24620  4860m 244116  3148m    0    0    0   83  10K  18K   5   4  85
    2.89  24600  4804m 244120  3149m    0    0    0   83  10K  18K   5   4  85
pmFetch: End of PCP archive

For complete information on pmstat usage and command line options, see the pmstat(1) man page.

4.2. The pmrep Command

The pmrep command displays performance metrics in ASCII tables, suitable for export into databases or report generators. It is a flexible command. For example, the following command provides continuous memory statistics on a host named surf:

pmrep -p -h surf kernel.all.load kernel.all.pswitch
          k.a.load  k.a.load  k.a.load  k.a.pswitch
          1 minute  5 minute  15 minut
                                           count/s
10:41:37     0.160     0.170     0.180          N/A
10:41:38     0.160     0.170     0.180     1427.016
10:41:39     0.160     0.170     0.180     2129.040
10:41:40     0.160     0.170     0.180     5335.163
10:41:41     0.160     0.170     0.180      723.125
10:41:42     0.140     0.160     0.180      591.859

See the pmrep(1) man page for more information.

4.3. The pmval Command

The pmval command dumps the current values for the named performance metrics. For example, the following command reports the value of performance metric proc.nprocs once per second (by default), and produces output similar to this:

pmval proc.nprocs
metric:    proc.nprocs
host:      localhost
semantics: instantaneous value
units:     none
samples:   all
interval:  1.00 sec
         81
         81
         82
         81

In this example, the number of running processes was reported once per second.

Where the semantics of the underlying performance metrics indicate that it would be sensible, pmval reports the rate of change or resource utilization.

For example, the following command reports idle processor utilization for each of four CPUs on the remote host dove, each five seconds apart, producing output of this form:

pmval -h dove -t 5sec -s 4 kernel.percpu.cpu.idle
metric:    kernel.percpu.cpu.idle
host:      dove
semantics: cumulative counter (converting to rate)
units:     millisec (converting to time utilization)
samples:   4
interval:  5.00 sec

cpu:1.1.0.a cpu:1.1.0.c cpu:1.1.1.a cpu:1.1.1.c
     1.000       0.9998      0.9998      1.000
     1.000       0.9998      0.9998      1.000
     0.8989      0.9987      0.9997      0.9995
     0.9568      0.9998      0.9996      1.000

Similarly, the following command reports disk I/O read rate every minute for just the disk /dev/disk1, and produces output similar to the following:

pmval -t 1min -i disk1 disk.dev.read
metric:    disk.dev.read
host:      localhost
semantics: cumulative counter (converting to rate)
units:     count (converting to count / sec)
samples:   indefinite
interval:  60.00 sec
        disk1
         33.67
         48.71
         52.33
         11.33
         2.333

The -r flag may be used to suppress the rate calculation (for metrics with counter semantics) and display the raw values of the metrics.

In the example below, manipulation of the time within the archive is achieved by the exchange of time control messages between pmval and pmtime.

pmval -g -a ${PCP_LOG_DIR}/pmlogger/myserver/20170731 kernel.all.load

The pmval command is documented by the pmval(1) man page, and annotated examples of the use of pmval can be found in the PCP Tutorials and Case Studies companion document.

4.4. The pminfo Command

The pminfo command displays various types of information about performance metrics available through the Performance Co-Pilot (PCP) facilities.

The -T option is extremely useful; it provides help text about performance metrics:

pminfo -T mem.util.cached
mem.util.cached
Help:
Memory used by the page cache, including buffered file data.
This is in-memory cache for files read from the disk (the pagecache)
but doesn't include SwapCached.

The -t option displays the one-line help text associated with the selected metrics. The -T option prints more verbose help text.

Without any options, pminfo verifies that the specified metrics exist in the namespace, and echoes those names. Metrics may be specified as arguments to pminfo using their full metric names. For example, this command returns the following response:

pminfo hinv.ncpu network.interface.total.bytes
hinv.ncpu
network.interface.total.bytes

A group of related metrics in the namespace may also be specified. For example, to list all of the hinv metrics you would use this command:

pminfo hinv
hinv.physmem
hinv.pagesize
hinv.ncpu
hinv.ndisk
hinv.nfilesys
hinv.ninterface
hinv.nnode
hinv.machine
hinv.map.scsi
hinv.map.cpu_num
hinv.map.cpu_node
hinv.map.lvname
hinv.cpu.clock
hinv.cpu.vendor
hinv.cpu.model
hinv.cpu.stepping
hinv.cpu.cache
hinv.cpu.bogomips

If no metrics are specified, pminfo displays the entire collection of metrics. This can be useful for searching for metrics, when only part of the full name is known. For example, this command returns the following response:

pminfo | grep nfs
nfs.client.calls
nfs.client.reqs
nfs.server.calls
nfs.server.reqs
nfs3.client.calls
nfs3.client.reqs
nfs3.server.calls
nfs3.server.reqs
nfs4.client.calls
nfs4.client.reqs
nfs4.server.calls
nfs4.server.reqs

The -d option causes pminfo to display descriptive information about metrics (refer to the pmLookupDesc(3) man page for an explanation of this metadata information). The following command and response show use of the -d option:

pminfo -d proc.nprocs disk.dev.read filesys.free
proc.nprocs
    Data Type: 32-bit unsigned int  InDom: PM_INDOM_NULL 0xffffffff
    Semantics: instant  Units: none

disk.dev.read
    Data Type: 32-bit unsigned int  InDom: 60.1 0xf000001
    Semantics: counter  Units: count

filesys.free
    Data Type: 64-bit unsigned int  InDom: 60.5 0xf000005
    Semantics: instant  Units: Kbyte

The -l option causes pminfo to display labels about metrics (refer to the pmLookupLabels(3) man page for an explanation of this metadata information). If the metric has an instance domain, the labels associated with each instance of the metric is printed. The following command and response show use of the -l option:

pminfo -l -h shard kernel.pernode.cpu.user
kernel.percpu.cpu.sys
    inst [0 or "cpu0"] labels
{"agent":"linux","cpu":0,"device_type":"cpu","domainname":"acme.com","groupid":1000,"hostname":"shard","indom_name":"per cpu","userid":1000}
    inst [1 or "cpu1"] labels
{"agent":"linux","cpu":1,"device_type":"cpu","domainname":"acme.com","groupid":1000,"hostname":"shard","indom_name":"per cpu","userid":1000}
    inst [2 or "cpu2"] labels
{"agent":"linux","cpu":2,"device_type":"cpu","domainname":"acme.com","groupid":1000,"hostname":"shard","indom_name":"per cpu","userid":1000}
    inst [3 or "cpu3"] labels
{"agent":"linux","cpu":3,"device_type":"cpu","domainname":"acme.com","groupid":1000,"hostname":"shard","indom_name":"per cpu","userid":1000}
    inst [4 or "cpu4"] labels
{"agent":"linux","cpu":4,"device_type":"cpu","domainname":"acme.com","groupid":1000,"hostname":"shard","indom_name":"per cpu","userid":1000}
    inst [5 or "cpu5"] labels
{"agent":"linux","cpu":5,"device_type":"cpu","domainname":"acme.com","groupid":1000,"hostname":"shard","indom_name":"per cpu","userid":1000}
    inst [6 or "cpu6"] labels
{"agent":"linux","cpu":6,"device_type":"cpu","domainname":"acme.com","groupid":1000,"hostname":"shard","indom_name":"per cpu","userid":1000}
    inst [7 or "cpu7"] labels
{"agent":"linux","cpu":7,"device_type":"cpu","domainname":"acme.com","groupid":1000,"hostname":"shard","indom_name":"per cpu","userid":1000}

The -f option to pminfo forces the current value of each named metric to be fetched and printed. In the example below, all metrics in the group hinv are selected:

pminfo -f hinv
hinv.physmem
    value 15701

hinv.pagesize
    value 16384

hinv.ncpu
    value 4

hinv.ndisk
    value 6

hinv.nfilesys
    value 2

hinv.ninterface
    value 8

hinv.nnode
    value 2

hinv.machine
    value "IP35"

hinv.map.cpu_num
    inst [0 or "cpu:1.1.0.a"] value 0
    inst [1 or "cpu:1.1.0.c"] value 1
    inst [2 or "cpu:1.1.1.a"] value 2
    inst [3 or "cpu:1.1.1.c"] value 3

hinv.map.cpu_node
    inst [0 or "node:1.1.0"] value "/dev/hw/module/001c01/slab/0/node"
    inst [1 or "node:1.1.1"] value "/dev/hw/module/001c01/slab/1/node"

hinv.cpu.clock
    inst [0 or "cpu:1.1.0.a"] value 800
    inst [1 or "cpu:1.1.0.c"] value 800
    inst [2 or "cpu:1.1.1.a"] value 800
    inst [3 or "cpu:1.1.1.c"] value 800

hinv.cpu.vendor
    inst [0 or "cpu:1.1.0.a"] value "GenuineIntel"
    inst [1 or "cpu:1.1.0.c"] value "GenuineIntel"
    inst [2 or "cpu:1.1.1.a"] value "GenuineIntel"
    inst [3 or "cpu:1.1.1.c"] value "GenuineIntel"

hinv.cpu.model
    inst [0 or "cpu:1.1.0.a"] value "0"
    inst [1 or "cpu:1.1.0.c"] value "0"
    inst [2 or "cpu:1.1.1.a"] value "0"
    inst [3 or "cpu:1.1.1.c"] value "0"

hinv.cpu.stepping
    inst [0 or "cpu:1.1.0.a"] value "6"
    inst [1 or "cpu:1.1.0.c"] value "6"
    inst [2 or "cpu:1.1.1.a"] value "6"
    inst [3 or "cpu:1.1.1.c"] value "6"

hinv.cpu.cache
    inst [0 or "cpu:1.1.0.a"] value 0
    inst [1 or "cpu:1.1.0.c"] value 0
    inst [2 or "cpu:1.1.1.a"] value 0
    inst [3 or "cpu:1.1.1.c"] value 0

hinv.cpu.bogomips
    inst [0 or "cpu:1.1.0.a"] value 1195.37
    inst [1 or "cpu:1.1.0.c"] value 1195.37
    inst [2 or "cpu:1.1.1.a"] value 1195.37
    inst [3 or "cpu:1.1.1.c"] value 1195.37

The -h option directs pminfo to retrieve information from the specified host. If the metric has an instance domain, the value associated with each instance of the metric is printed:

pminfo -h dove -f filesys.mountdir
filesys.mountdir
    inst [0 or "/dev/xscsi/pci00.01.0/target81/lun0/part3"] value "/"
    inst [1 or "/dev/xscsi/pci00.01.0/target81/lun0/part1"] value "/boot/efi"

The -m option prints the Performance Metric Identifiers (PMIDs) of the selected metrics. This is useful for finding out which PMDA supplies the metric. For example, the output below identifies the PMDA supporting domain 4 (the leftmost part of the PMID) as the one supplying information for the metric environ.extrema.mintemp:

pminfo -m environ.extrema.mintemp
environ.extrema.mintemp PMID: 4.0.3

The -v option verifies that metric definitions in the PMNS correspond with supported metrics, and checks that a value is available for the metric. Descriptions and values are fetched, but not printed. Only errors are reported.

Complete information on the pminfo command is found in the pminfo(1) man page. There are further examples of the use of pminfo in the PCP Tutorials and Case Studies.

4.5. The pmstore Command

From time to time you may wish to change the value of a particular metric. Some metrics are counters that may need to be reset, and some are simply control variables for agents that collect performance metrics. When you need to change the value of a metric for any reason, the command to use is pmstore.

Note

For obvious reasons, the ability to arbitrarily change the value of a performance metric is not supported. Rather, PCP collectors selectively allow some metrics to be modified in a very controlled fashion.

The basic syntax of the command is as follows:

pmstore metricname value

There are also command line flags to further specify the action. For example, the -i option restricts the change to one or more instances of the performance metric.

The value may be in one of several forms, according to the following rules:

  1. If the metric has an integer type, then value should consist of an optional leading hyphen, followed either by decimal digits or “0x” and some hexadecimal digits; “0X” is also acceptable instead of “0x.”

  2. If the metric has a floating point type, then value should be in the form of an integer (described above), a fixed point number, or a number in scientific notation.

  3. If the metric has a string type, then value is interpreted as a literal string of ASCII characters.

  4. If the metric has an aggregate type, then an attempt is made to interpret value as an integer, a floating point number, or a string. In the first two cases, the minimal word length encoding is used; for example, “123” would be interpreted as a four-byte aggregate, and “0x100000000” would be interpreted as an eight-byte aggregate.

The following example illustrates the use of pmstore to enable performance metrics collection in the txmon PMDA (see ${PCP_PMDAS_DIR}/txmon for the source code of the txmon PMDA). When the metric txmon.control.level has the value 0, no performance metrics are collected. Values greater than 0 enable progressively more verbose instrumentation.

pminfo -f txmon.count
txmon.count
No value(s) available!
pmstore txmon.control.level 1
txmon.control.level old value=0 new value=1
pminfo -f txmon.count
txmon.count
       inst [0 or "ord-entry"] value 23
       inst [1 or "ord-enq"] value 11
       inst [2 or "ord-ship"] value 10
       inst [3 or "part-recv"] value 3
       inst [4 or "part-enq"] value 2
       inst [5 or "part-used"] value 1
       inst [6 or "b-o-m"] value 0

For complete information on pmstore usage and syntax, see the pmstore(1) man page.