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Performance Management Guide
It is not enough to create the most efficient possible individual
programs. In many cases, the actual programs being run were created
outside of the control of the person who is responsible for meeting the
organization's performance objectives. Further, most of the levels
of the hierarchy described in Program Execution Dynamics
are managed by one or more parts of the operating system. In any case,
after the application programs have been acquired, or implemented as
efficiently as possible, further improvement in the overall performance of the
system becomes a matter of system tuning. The main components that are
subject to system-level tuning are:
- Communications I/O
- Depending on the type of workload and the type of communications link, it
might be necessary to tune one or more of the communications device drivers,
TCP/IP, or NFS.
- Fixed Disk
- The Logical Volume Manager (LVM) controls the placement of file systems
and paging spaces on the disk, which can significantly affect the amount of
seek latency the system experiences. The disk device drivers control
the order in which I/O requests are acted on.
- Real Memory
- The Virtual Memory Manager (VMM) controls the pool of free real-memory
frames and determines when and from whom to steal frames to replenish the
pool.
- Running Thread
- The scheduler determines which dispatchable entity should next receive
control. In AIX Version 4, the dispatchable entity changes from a
process to a thread. See Thread Support.
Workloads tend to fall naturally into a small number of classes. The
types listed below are sometimes used to categorize systems. However,
because a single system is often called upon to process multiple classes,
workload seems more apt in the context of performance.
- Multiuser
- A workload that consists of a number of users submitting work through
individual terminals. Typically, the performance objectives of such a
workload are either to maximize system throughput while preserving a specified
worst-case response time or to obtain the best possible response time for a
fairly constant workload.
- Server
- A workload that consists of requests from other systems. For
example, a file-server workload is mostly disk read/write requests. In
essence, it is the disk-I/O component of a multiuser workload (plus NFS or
other I/O activity), so the same objective of maximum throughput within a
given response-time limit applies. Other server workloads consist of
compute-intensive programs, database transactions, printer jobs, and so
on.
- Workstation
- A workload that consists of a single user submitting work through the
native keyboard and receiving results on the native display of the
system. Typically, the highest-priority performance objective of such a
workload is minimum response time to the user's requests.
When a single system is processing workloads of more than one type, a clear
understanding must exist between the users and the performance analyst as to
the relative priorities of the possibly conflicting performance objectives of
the different workloads.
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