OS/2 Shareware BBS: 14 Text/14-Text.zip/os2v1.zip/ART1.TXT

Text File | 1994-03-26 | 12KB | 242 lines

System Monitoring in Multitasking Environments

By Dave Wallenberg
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The focus of this article is to discuss the value of monitoring system
activities in the multitasking and multithreading environment as it
pertains to such operating systems such as OS/2, UNIX, and NT.


OS/2, UNIX, and NT are multitasking and multithreading operating systems.
This means that more than one task can be performed at a time.  Not only
does this imply that the user can work on more than one thing at a time,
but the operating system itself takes advantage of this as well and has
several processes executing in the background.  These processes are typi-
cally hidden from the user.

Where there can be numerous activities, there can be several resources and
devices being used simultaneously.  This adds a level of complexity that
today's user needs to be aware of.  The user may need to be aware of or
desire the ability to monitor:

     CPU usage to identify and resolve performance bottlenecks.  This can
     be invaluable when trying to understand why and when your system runs
     slow and the ability to identify what processes cause the degradation.

     With memory utilization and how much memory is currently in use, one
     can gain insight into system tuning.  The more components that are
     simultaneously active, the more memory is demanded until excess swap-
     ping occurs.

     Swap utilization to identify excess and frequent swap activity when
     memory is over committed.  This can be a good identifier for needing
     more memory.  When physical memory is exceeded based on the programs
     simultaneously running and their memory requirements, the operating
     system responds by temporarily "moving" pieces (4KB pages) of less
     active memory out to disk.  These chunks of memory are brought back
     into memory when the memory is referenced.  A Swap monitor can provide
     insight into excess swapping.

     Program performance can enable the user to assess the impact of run-
     ning program(s).  Today's diverse software and multimedia craze re-
     quires the high performance of at least a i486 based or equivalent
     processor to keep up with CPU and memory intensive applications.  The
     ability to examine the CPU usage of a program can help identify de-
     manding programs and perhaps ill-behaved programs.  Program monitoring
     can also offer the ability to see the number programs active and what
     state each program is in.

     Disk space utilization is often desirable to monitor.  How many people
     out there have more disk space than they know what to do with.  Most
     people are always "tight" on disk space.  As you are downloading a large
     file, or excess Swapping occurs, the ability to quickly view your disk
     space constraints can be very valuable.

     Status of print spooler and print queue(s) is another valuable item to
     monitor.  Particularly when the computer can print to LAN printers,
     receive and send fax documents, and more.

     The current date, time, disk drives online and available, and more.


The three most important things in a computer have never changed.  They
remain, and in the following sequence, are:

     1.  The speed of the processor(s)
     2.  The amount, speed, and location of physical memory
     3.  The amount and speed of external storage disk


Program and CPU Monitoring:
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The multitasking and multithreading environment of OS/2 allows numerous
activities to execute simultaneously.  Although each process executing
appears to be sharing the same CPU concurrently, the processes are actually
being individual time-slices from the OS/2 Scheduler in what is called a
Priority driven Round-Robin algorithm.  This means the scheduler factors
into the time-slice algorithm (amongst other items such as I/O vs CPU bound
and Min/Max time-slice milliseconds) the priority of each thread within a
process.  The information that the operating system maintains and collects
per process and each thread within the process is stored in the Process
Tables.  These tables are memory resident data structures that only the
operating system can access OS/2 provides an (undocumented) API that allows
access to the Process Table information. With this, the monitoring software
can summarize and report the statistics in a meaningful presentation.  Some
of the data that can be monitored and presented to the user is:

     Number of processes and threads that are running

     The priority and state of the thread in a process

     The amount of CPU time each thread of a process has received

     Which CPU each thread is attached to in the SMP (Symmetric Multi-
     Processing) version

     and more...


These items form the basis for monitoring programs executing, how they are
executing, and what amount of CPU each is consuming.  This information, if
presented intuitively, can be useful to any audience.  Whether the user be a
novice or a software engineer, this real-time summary provides insight.  It
can be used as resolving overall system performance or performance right down
to the thread level.  For example, when the system appears to be "hung" or
sluggish, a simple system-wide CPU monitor can inform the user as to the
extent of unresponsiveness.  The ability to then "zoom" into a birds-eye
view of all programs running and examine the CPU utilization per processes,
usually will identify the culprit program.

Without this insight, you're at a complete loss as to what happened.  The
CPU monitor is typically the first monitor tool to obtain and rather simple
to develop.  But the Process Monitor is difficult to develop and depends
solely on the ability to "get at" the Process Table information of the opera-
ting system.  The Process Table(s) structure is operating system specific and
requires a strong understanding of the structure layout.  Most new operating
systems provide this raw data for applications in the form of an API. OS/2
provides much of the data to the monitoring application via an API called
DosQProcStatus.

At it's best, the monitoring tool may provide an Early Warning mechanism.
This ability would warn the user when certain thresholds have been exceeded.
Such as abnormal and excessive CPU usage may indicate a runaway situation.
Before this condition brings the entire system to its knees, the user can
have he opportunity to not only terminate the ill-behaved culprit, but more
importantly, determine the cause.  Early Warning mechanisms are seen most
often in real-time mission-critical systems.


Memory Monitor:
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The real-time memory monitor is valuable in providing the user with insight
into the amount of memory that is currently in use and memory that is idle
and subject to being swapped-out.

In a virtual memory model such as OS/2, the amount of actual free memory is
very difficult to determine and usually calculates into an approximation.
The virtual memory model simply looks at available memory as physical memory
installed plus disk space available.  So free memory can be two different
things; Actual free physical memory, or total virtual memory.  Actual free
memory is most often desired to monitor.

Tracking free physical memory, along with swap activity, enables you to
determine whether you have enough memory to meet your demands.  This is pri-
marily an issue of cost.  Although, some may interpret it as an issue of
"pain".  What is your "threshold of pain" while you wait for the system to
swap out memory pages to free up room for your next program?


Disk and Swap Monitoring:
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Swapping is very much related to the amount of physical memory available.
At some point in the tuning process you determine your "threshold of pain".
RAM costs money, but swapping is inevitable - and normal.  Unless your appli-
cation is of a time-critical nature and can not afford ANY swap time.

The ability to monitor the frequency and degree of swapping can be the only
thing you need in order to tune a system.  With this alone, you can do a per-
formance tune-up on a given system.  Or at least identify if more memory is
needed and how much.


Monitor Logging:
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Only surface analysis tuning can be accomplished without the ability to re-
cord the monitoring activities.  Periodic and continuous logging are a must
for the monitoring tool.

After logging activity for a given amount of time, you have captured a sample
set of statistics.  This raw data can be summarized and produce minimum,
maximum, and average performance reports over different time intervals.  Per-
haps peak periods.

It is important that a time-stamp is placed in the log (preferably down to a
hundredth of a second).  This facilitates even the most stressful situations
such as real-time monitoring.


Monitor Caveats:
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The monitoring software can not cause overhead.  To accomplish many of the
monitoring tasks discussed in this article, the monitoring software is
required to periodically sample the device or system resource.  Obviously,
the more often samplings occur, the more system resources are used by the
monitoring software.  The ideal monitoring software:

     Is designed to run ALL the time and causes absolutely no interruptions.
     Realizing that the PC workstation is used by the user and the typical
     user uses the keyboard, keyboard and video delays caused by the monitor-
     ing software means that the monitoring software is using too much CPU to
     accomplish its job.

     Is designed to handle a stand-alone environment as well as being capable
     of monitoring resources in a intensive real-time environment as well.

     Is designed to be aware of LAN connectivity.

     Is designed to allow adjustable sampling rates for each resource to be
     monitored.

     Sampling each resource should be staggered to avoid sampling ALL
     resources at the same time.  This can also be accomplished by the user
     by adjusting the frequency of sampling.

     Exercises multithreading capabilities of the operating system so
     resource intensive tasks can execute at idle priorities.

     Is self-contained and integrated.

     Contains a logging mechanism.  This is very important for unattended
     operations.  Once again, and easy to overlook, is how the logging is
     accomplished and should cause no extra overhead.

Run one CPU monitor at a time.  Attempting to run multiple CPU monitors at
the same time defeats the purpose and causes each monitor to absorb the
other's CPU load.

Depending on how robust and feature rich the monitoring software is, the
software may not be able to guarantee 100% compatibility with future versions
of the operating system.  Due to the nature of monitoring and the uniqueness
of the application, most monitoring software requires slight modification per
operating system release.  Contact the vendor before you migrate to a new
release of the operating system.  The monitoring software is not usually
affected by minor OS upgrade versions.



About the Author:
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Mr. Wallenberg is a senior consultant with Computer Sciences Corporation and
specializes in OS/2 and UNIX based systems programming.  Independently he
develops OS/2 and UNIX system monitoring tools.  His latest creation is PM
Patrol for OS/2 which provides much of the items discussed in this article.
Mr. Wallenberg can be contacted via CompuServe (72702,2320) or the Internet
([e-mail]).