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Chapter 3. Bandwidth and Processing Power

3.3.2. Monitoring CPU Utilization on Red Hat Linux

Unlike bandwidth, monitoring CPU utilization is much more straightforward. From a single percent 

age of CPU utilization in GNOME System Monitor, to the more in depth statistics reported by

sar

,

it is possible to accurately determine how much CPU power is being consumed and by what.

Moving beyond GNOME System Monitor,

top

is the first resource monitoring tool discussed in

Chapter 2 Resource Monitoring to provide a more in depth representation of CPU utilization. Here is

a

top

report from a dual processor workstation:

9:44pm

up 2 days, 2 min,

1 user,

load average: 0.14, 0.12, 0.09

90 processes: 82 sleeping, 1 running, 7 zombie, 0 stopped

CPU0 states:

0.4% user,

1.1% system,

0.0% nice, 97.4% idle

CPU1 states:

0.5% user,

1.3% system,

0.0% nice, 97.1% idle

Mem:

1288720K av, 1056260K used,

232460K free,

0K shrd,

145644K buff

Swap:

522104K av,

0K used,

522104K free

469764K cached

PID USER

PRI

NI

SIZE

RSS SHARE STAT %CPU %MEM

TIME COMMAND

30997 ed

16

0

1100 1100

840 R

1.7

0.0

0:00 top

1120 root

5  10

249M 174M 71508 S <

0.9 13.8 254:59 X

1260 ed

15

0 54408

53M

6864 S

0.7

4.2

12:09 gnome terminal

888 root

15

0

2428 2428

1796 S

0.1

0.1

0:06 sendmail

1264 ed

15

0 16336

15M

9480 S

0.1

1.2

1:58 rhn applet gui

1 root

15

0

476

476

424 S

0.0

0.0

0:05 init

2 root

0K

0

0

0

0 SW

0.0

0.0

0:00 migration_CPU0

3 root

0K

0

0

0

0 SW

0.0

0.0

0:00 migration_CPU1

4 root

15

0

0

0

0 SW

0.0

0.0

0:01 keventd

5 root

34

19

0

0

0 SWN

0.0

0.0

0:00 ksoftirqd_CPU0

6 root

34

19

0

0

0 SWN

0.0

0.0

0:00 ksoftirqd_CPU1

7 root

15

0

0

0

0 SW

0.0

0.0

0:05 kswapd

8 root

15

0

0

0

0 SW

0.0

0.0

0:00 bdflush

9 root

15

0

0

0

0 SW

0.0

0.0

0:01 kupdated

10 root

25

0

0

0

0 SW

0.0

0.0

0:00 mdrecoveryd

The first CPU related information is present on the very first line: the load average. The load average

is a number that corresponds to the average number of runnable processes on the system. The load

average is often listed as three sets of numbers (as seen here), which represent the load average for the

past 1, 5, and 15 minutes, indicating that the system in this example was not very busy.

The next line, although not strictly related to CPU utilization, has an indirect relationship, in that

it shows the number of runnable processes (here, only one    remember this number, as it means

something special in this example). The number of runnable processes is a good indicator of how

CPU bound a system might be.

Next are two lines that display the current utilization for each of the two CPUs in the system. The

utilization statistics are broken down to show whether the CPU cycles expended were done so for

user level or system level processing; also included is a statistic showing how much CPU time was

expended by processes with altered scheduling priorities. Finally, there is an idle time statistic.

Moving down into the process related section of the display, we find that the process using the most

CPU power is

top

itself; in other words, the one runnable process on this otherwise idle system was

top

taking a "picture" of itself.

Tip

It is important to remember that the very act of running a system monitor affects the resource utiliza 

tion statistics you receive. All software based monitors do this to some extent.