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DA1000.FAX
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1994-12-03
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Dropped connections: emulators, fax, etc 7/18/94
FILE: OSDA1000.FAX - 5/11/94
TITLE: 940504 INTERRUPT RATE GREATER THAN 1000/SEC FOR A
VIRTUAL DOS MACHINE (VDM) - OS/2 2.x
DESCRIPTION OF SYMPTONS:
I/O Problems running DOS emulation, fax,
telecommunication real-time interrupt driven, and
other timing sensitive programs.
SUMMARY OF RESOLUTION:
1) We have found that customers using higher speed CPUs tend
not to have these problems because VDMs are running more
often, and thus receive the virtualized interrupts more
frequently. Slower CPUs are more likely to experience
problems with DOS I/O bound applications running in VDMs.
The most common applications experiencing these problems
are: DOS Emulation software products such as IBM PC 3270,
IBM Enhanced 5250, Attachmate Extra for DOS and Windows,
etc. DOS Fax programs, DOS telecommunciation programs, DOS
programs that rely on real-time interrupt driven I/O
processing and other highly timing sensitive I/O bound DOS
applications. These applications are most likely to fail
with dropped connections, communication data-loss, time-out
errors, etc.
2) IBM Management has approved closure of APAR PJ03990 as a
SUG.
3) Closure of this APAR as SUG (suggestion) means that this
issue will go on to the OS/2 Planners for consideration in
future versions of the operating system. OS/2 v2.x is
working as designed. IBM Marketing Representatives may
submit Design Change Requests (DCRs) in order to request
changes to the design of OS/2 to allow for better
performance concerning the handling Virtual DOS Machine
(VDM) interrupts.
4) For more information concerning the design of OS/2 and
Virtual DOS Machine interrupt handling, please consult the
book entitled "The Design of OS/2" by H.M. Deitel and M.S.
Kogan. ISBN #0-201-54889-5. Pages 290-291, Section 10.4,
and Page 299, Section 10.4.5.
5) While changes to the design of future versions of
OS/2 are being considered by the OS/2 Planners,
customers should try to obtain an OS/2 version of the
application that is not working as they would like
it to. For example, there are many OS/2 3270 and
5250 products on the market, such as IBM's own
Communications Manager. There are many OS/2-based
FAX and telecommunication programs to choose from also.
Check for listings of OS/2 applications along with the
vendors names and phone numbers on Compuserve (a great
source of this information exists in a file called
APPOS2.ZIP in IBM's IBMOS2 section). Otherwise contact the
vendor of the application and request an OS/2-specific
version. Most vendors are very receptive to new market
opportunities! Give them a call!
6) OS/2 2.x's current design restricts the number of VDM-bound
interrupts that can be handled efficiently due to the
virtualized nature of the interrupt delivery system.
However, this does provide for better system security and
allows for other advantages as well (please see the book
referenced above). OS/2's Planners must now decide whether
to change the design of OS/2 and have a change implemented
in a future release of the operating system. Again, OS/2
v2.x is working as designed.
Report by: OS/2 Dosap Analyst Team - 05/94
IBM - Boca Raton, Florida
12/31/99