Performance Tuning -- The vmstat Tool
Contents
About this document
Related documentation
About vmstat
Summary statistics
About this document
This document provides an overview of the output of the
vmstat. This information applies to AIX Versions 4.x.
Related documentation
The fields produced by
the s, f, and [Drives] options of vmstat are fully
documented in the AIX Performance Tuning Guide, publication number
SC23-2365, and in the online product documentation.
The product documentation library is also available:
http://www.rs6000.ibm.com/resource/aix_resource/Pubs/index.html
About vmstat
Although a system may have sufficient real resources, it may
perform below expectations if logical resources are not
allocated properly.
Use vmstat to determine real and logical resource utilization.
It samples kernel tables and counters and then normalizes
the results and presents them in an appropriate format.
By default, vmstat sends its report to standard out, but it
can be run with the output redirected.
vmstat is normally invoked with an interval and a count
specified. The interval is the length of time in seconds
over which vmstat is to gather and report data. The count
is the number of intervals to run. If no parameters are
specified, vmstat will report a single record of statistics
for the time since the system was booted. There may have been inactivity
or fluctuations in the workload, so the results may not represent
current activity. Be aware that the first record in
the output presents statistics since the last boot (except when
invoked with the -f or -s option). In many instances, this
data can be ignored.
vmstat reports statistics about processes, virtual memory,
paging activity, faults, CPU activity, and disk transfers.
Options and parameters recognized by this tool are indicated
by the usage prompt:
vmstat [-fs] [Drives] [Interval] [Count]
The following figure lists output where the smallest work
unit is called a kernel thread (kthr). The r and b
under this column represent the number of "threads", not
processes, placed on these queues.
--------------------------------------------------------------------
| |
| kthr memory page faults cpu |
| ----- -------- ----------------- -------------- ----------- |
| r b avm fre re pi po fr sr cy in sy cs us sy id wa |
| 0 0 6747 1253 0 0 0 0 0 0 114 10 22 0 1 26 0 |
| 1 0 6747 1253 0 0 0 0 0 0 113 118 43 17 4 79 0 |
| 0 0 6747 1253 0 0 0 0 0 0 118 99 33 8 3 89 0 |
| |
--------------------------------------------------------------------
Figure: Sample output from vmstat 1 3
kthr
memory
page
faults
cpu
Summary statistics
vmstat with the -s option reports absolute counts of various
events since the system was booted. There are 23 separate
events reported in the vmstat -s output; the following 4
have proven most helpful. The 19 remaining fields
contain a variety of activities from address translation
faults to lock misses to system calls. The information in
those 19 fields is also valuable but is less frequently
used.
page ins
The page ins field shows the number systemwide page-ins.
When a page is read from disk to memory, this count is
incremented. It is a count of VMM-initiated read operations
and, with the page outs field, represents the real I/O (disk
reads and writes) initiated by the VMM.
page outs
The page outs field shows the number of systemwide page-outs.
The process of writing pages to the disk is count incremented.
The page outs field value is a total count of VMM-initiated
write operations
and, with the page ins field, represents the total
amount of real I/O initiated by the VMM.
paging space page ins
The paging space page ins field is the count of ONLY pages
read from paging space.
paging space page outs
The paging space page outs field is the count of ONLY
pages written to paging space.
Using the summary statistics
The four preceding fields can be used to indicate how much of
the system's I/O is for persistent storage. If the value
for paging space page ins is subtracted from the
(systemwide) value for page ins, the result is the
number of pages that were read from persistent storage
(files). Likewise, if the value for paging space page outs
is subtracted from the (systemwide) value for page outs, the
result is the number of persistent pages (files) that
were written to disk.
Remember that these counts apply to the time since system initialization. If
you need counts for a given time interval, execute vmstat
-s at the time you want to start monitoring and again at
the end of the interval. The deltas between like fields of
successive reports will be the count for the interval. It
is easier to redirect the output of the reports to a file
and then perform the math.
[ Doc Ref: 90605226914708 Publish Date: Dec. 05, 2000 4FAX Ref: 6220 ]