AIX 5L Problem Determination - IBM Redbooks

control, the blocked column (b) in the vmstat command report indicates the
increase in the number of threads rather than the run queue.
The cpu columns
The four right-hand columns are a breakdown, in percentage of CPU time used,
of user threads, system threads, CPU idle time (running the wait process), and
CPU idle time when the system had outstanding disk or NFS I/O requests.
The us column
The us column shows the percent of CPU time spent in user mode. A UNIX
process can execute in either user mode or system (kernel) mode. When in user
mode, a process executes within its application code and does not require kernel
resources to perform computations, manage memory, or set variables.
The sy column
The sy column details the percentage of time the CPU was executing a process
in system mode. This includes CPU resource consumed by kernel processes
(kprocs) and others that need access to kernel resources. If a process needs
kernel resources, it must execute a system call, and is thereby switched to
system mode to make that resource available. For example, reading or writing of
a file requires kernel resources to open the file, seek a specific location, and read
or write data, unless memory mapped files are used.
The id column
The id column shows the percentage of time that the CPU is idle, or waiting,
without pending local disk I/O. If there are no processes available for execution
(the run queue is empty), the system dispatches a process called wait. On an
SMP system, one wait process per processor can be dispatched. On a
uniprocessor system, the process ID (PID) is usually 516. SMP systems will have
an idle kproc for each processor. If the ps command report shows a high
aggregate time for this process, it means there were significant periods of time
when no other process was ready to run or waiting to be executed on the CPU.
The system was therefore mostly idle and waiting for new tasks.
If there are no I/Os pending to a local disk, all time charged to wait is classified as
idle time. In AIX Version 4.3.2 and earlier, an access to remote disks
(NFS-mounted disks) is treated as idle time (with a small amount of sy time to
execute the NFS requests) because there is no pending I/O request to a local
disk. With AIX Version 4.3.3 and later, NFS goes through the buffer cache, and
waits in those routines are accounted for in the wa statistics.
The wa column
The wa column details the percentage of time the CPU was idle with pending
local disk I/O (this is also true for NFS-mounted disks in AIX Version 4.3.3 and
Chapter 10. Performance problem determination 239