CPU与iostat

中央处理器（CPU，central processing unit）作为计算机系统的运算和控制核心，是信息处理、程序运行的最终执行单元。CPU是计算机的运算和控制核心。计算机系统中所有软件层的操作，最终都通过指令集映射为CPU的操作。

 

NAME
       iostat - Report Central Processing Unit (CPU) statistics and input/output statistics for devices and partitions.

SYNOPSIS
       iostat [ -c ] [ -d ] [ -h ] [ -k | -m ] [ -N ] [ -t ] [ -V ] [ -x ] [ -y ] [ -z ] [ -j { ID | LABEL | PATH | UUID | ... } ] [ [
       -T ] -g group_name ] [ -p [ device [,...] | ALL ] ] [ device [...] | ALL ] [ interval [ count ] ]

DESCRIPTION
       The iostat command is used for monitoring system input/output device loading by observing the time the devices  are  active  in
       relation  to their average transfer rates. The iostat command generates reports that can be used to change system configuration
       to better balance the input/output load between physical disks.

       The first report generated by the iostat command provides statistics concerning the time since the system  was  booted,  unless
       the  -y option is used (in this case, this first report is omitted).  Each subsequent report covers the time since the previous
       report. All statistics are reported each time the iostat command is run. The report consists of a CPU header row followed by  a
       row of CPU statistics. On multiprocessor systems, CPU statistics are calculated system-wide as averages among all processors. A
       device header row is displayed followed by a line of statistics for each device that is configured.

       The interval parameter specifies the amount of time in seconds between each report. The first report  contains  statistics  for
       the  time  since  system  startup (boot), unless the -y option is used (in this case, this report is omitted).  Each subsequent
       report contains statistics collected during the interval since the previous report. The count parameter  can  be  specified  in
       conjunction  with  the  interval  parameter.  If  the count parameter is specified, the value of count determines the number of
       reports generated at interval seconds apart. If the interval parameter is specified without the  count  parameter,  the  iostat
       command generates reports continuously.

REPORTS
       The iostat command generates two types of reports, the CPU Utilization report and the Device Utilization report.

       CPU Utilization Report
              The first report generated by the iostat command is the CPU Utilization Report. For multiprocessor systems, the CPU val‐
              ues are global averages among all processors.  The report has the following format:

              %user
                     Show the percentage of CPU utilization that occurred while executing at the user level (application).

              %nice
                     Show the percentage of CPU utilization that occurred while executing at the user level with nice priority.

              %system
                     Show the percentage of CPU utilization that occurred while executing at the system level (kernel).

              %iowait
                     Show the percentage of time that the CPU or CPUs were idle during which the system had an  outstanding  disk  I/O
                     request.

              %steal
                     Show the percentage of time spent in involuntary wait by the virtual CPU or CPUs while the hypervisor was servic‐
                     ing another virtual processor.

              %idle
                     Show the percentage of time that the CPU or CPUs were idle and the system did not have an  outstanding  disk  I/O
                     request.

       Device Utilization Report
              The  second  report generated by the iostat command is the Device Utilization Report. The device report provides statis‐
              tics on a per physical device or partition basis. Block devices and partitions for which statistics are to be  displayed
              may  be  entered  on  the  command line.  If no device nor partition is entered, then statistics are displayed for every
              device used by the system, and providing that the kernel maintains statistics for it.  If the ALL keyword  is  given  on
              the  command line, then statistics are displayed for every device defined by the system, including those that have never
              been used.  Transfer rates are shown in 1K blocks by default, unless the environment variable POSIXLY_CORRECT is set, in
              which case 512-byte blocks are used.  The report may show the following fields, depending on the flags used:

              Device:
                     This column gives the device (or partition) name as listed in the /dev directory.

              tps
                     Indicate  the  number of transfers per second that were issued to the device. A transfer is an I/O request to the
                     device. Multiple logical requests can be combined into a single I/O request to the device. A transfer is of inde‐
                     terminate size.

              Blk_read/s (kB_read/s, MB_read/s)
                     Indicate  the amount of data read from the device expressed in a number of blocks (kilobytes, megabytes) per sec‐
                     ond. Blocks are equivalent to sectors and therefore have a size of 512 bytes.

              Blk_wrtn/s (kB_wrtn/s, MB_wrtn/s)
                     Indicate the amount of data written to the device expressed in a number of blocks (kilobytes, megabytes) per sec‐
                     ond.

              Blk_read (kB_read, MB_read)
                     The total number of blocks (kilobytes, megabytes) read.

              Blk_wrtn (kB_wrtn, MB_wrtn)
                     The total number of blocks (kilobytes, megabytes) written.
              rrqm/s
                     The number of read requests merged per second that were queued to the device.

              wrqm/s
                     The number of write requests merged per second that were queued to the device.

              r/s
                     The number (after merges) of read requests completed per second for the device.

              w/s
                     The number (after merges) of write requests completed per second for the device.

              rsec/s (rkB/s, rMB/s)
                     The number of sectors (kilobytes, megabytes) read from the device per second.

              wsec/s (wkB/s, wMB/s)
                     The number of sectors (kilobytes, megabytes) written to the device per second.

              avgrq-sz
                     The average size (in sectors) of the requests that were issued to the device.

              avgqu-sz
                     The average queue length of the requests that were issued to the device.

              await
                     The  average  time  (in  milliseconds) for I/O requests issued to the device to be served. This includes the time
                     spent by the requests in queue and the time spent servicing them.

              r_await
                     The average time (in milliseconds) for read requests issued to the device to be served. This  includes  the  time
                     spent by the requests in queue and the time spent servicing them.

              w_await
                     The  average  time (in milliseconds) for write requests issued to the device to be served. This includes the time
                     spent by the requests in queue and the time spent servicing them.

              svctm
                     The average service time (in milliseconds) for I/O requests that were issued to the device. Warning! Do not trust
                     this field any more.  This field will be removed in a future sysstat version.

              %util
                     Percentage  of  elapsed  time  during which I/O requests were issued to the device (bandwidth utilization for the
                     device). Device saturation occurs when this value is close to 100%.

OPTIONS
       -c     Display the CPU utilization report.

       -d     Display the device utilization report.

       -g group_name { device [...] | ALL }
              Display statistics for a group of devices.  The iostat command reports statistics for each individual device in the list
              then  a  line of global statistics for the group displayed as group_name and made up of all the devices in the list. The
              ALL keyword means that all the block devices defined by the system shall be included in the group.

       -h     Make the Device Utilization Report easier to read by a human.

       -j { ID | LABEL | PATH | UUID | ... } [ device [...] | ALL ]
              Display persistent device names. Options ID, LABEL, etc. specify the type of the persistent name. These options are  not
              limited, only prerequisite is that directory with required persistent names is present in /dev/disk.  Optionally, multi‐
              ple devices can be specified in the chosen persistent name type.  Because persistent  device  names  are  usually  long,
              option -h is enabled implicitly with this option.

       -k     Display statistics in kilobytes per second.

       -m     Display statistics in megabytes per second.

       -N     Display the registered device mapper names for any device mapper devices.  Useful for viewing LVM2 statistics.

 

       -p [ { device [,...] | ALL } ]
              The  -p  option displays statistics for block devices and all their partitions that are used by the system.  If a device
              name is entered on the command line, then statistics for it and all its partitions are displayed. Last, the ALL  keyword
              indicates that statistics have to be displayed for all the block devices and partitions defined by the system, including
              those that have never been used. If option -j is defined before this option, devices entered on the command line can  be
              specified with the chosen persistent name type.

       -T     This option must be used with option -g and indicates that only global statistics for the group are to be displayed, and
              not statistics for individual devices in the group.

       -t     Print the time for each report displayed. The timestamp format may depend on the value of the S_TIME_FORMAT  environment
              variable (see below).

       -V     Print version number then exit.

       -x     Display extended statistics.

       -y     Omit first report with statistics since system boot, if displaying multiple records at given interval.

       -z     Tell iostat to omit output for any devices for which there was no activity during the sample period.

 

ENVIRONMENT
       The iostat command takes into account the following environment variables:

       S_TIME_FORMAT
              If  this  variable  exists  and  its  value is ISO then the current locale will be ignored when printing the date in the
              report header. The iostat command will use the ISO 8601 format  (YYYY-MM-DD)  instead.   The  timestamp  displayed  with
              option -t will also be compliant with ISO 8601 format.

       POSIXLY_CORRECT
              When this variable is set, transfer rates are shown in 512-byte blocks instead of the default 1K blocks.

EXAMPLES
       iostat
              Display a single history since boot report for all CPU and Devices.

       iostat -d 2
              Display a continuous device report at two second intervals.

       iostat -d 2 6
              Display six reports at two second intervals for all devices.

       iostat -x sda sdb 2 6
              Display six reports of extended statistics at two second intervals for devices sda and sdb.

       iostat -p sda 2 6
              Display six reports at two second intervals for device sda and all its partitions (sda1, etc.)

BUGS
       /proc filesystem must be mounted for iostat to work.

       Kernels older than 2.6.x are no longer supported.

       The  average service time (svctm field) value is meaningless, as I/O statistics are now calculated at block level, and we don't
       know when the disk driver starts to process a request. For this reason, this field will be removed in a future sysstat version.

FILES
       /proc/stat contains system statistics.

       /proc/uptime contains system uptime.

       /proc/diskstats contains disks statistics.

       /sys contains statistics for block devices.

       /proc/self/mountstats contains statistics for network filesystems.

       /dev/disk contains persistent device names.

AUTHOR
       Sebastien Godard (sysstat <at> orange.fr)

SEE ALSO
       sar(1), pidstat(1), mpstat(1), vmstat(8), nfsiostat(1), cifsiostat(1)