PSF for AIX V2: PSF Direct performance problem
ITEM: RTA000090444
Q:
ABSTRACT: PSF for AIX V2: PSF Direct performance problem
SEARCH ARG: psf/6000
TOPIC THREAD: PRINT
AFP
PSF6000
..
We are having a performance problem with a PSF Direct installation.
We have a 3835 attached to PSF for AIX V2 from PSF/MVS through a 3174.
The printer is printing a couple of pages, stopping for about a second
and then printing a few more pages. No error messages are generated
when this happens. It works okay for printing local AIX jobs.
Do you have any ideas on what might be causing this? The printer
is running very slowly as a result.
A:
Here are a few thoughts about performance in PSF Direct configurations:
1) Gathering traces can degrade throughput, sometimes dramatically.
You should ensure that you are not gathering any PSF Direct traces,
SNA Server/6000 link station traces, or PSF/MVS traces.
To determine whether you are gathering any PSF Direct traces,
use smit to view the "Error Log and Trace Options" for the printer
used by PSF Direct. The "ACTIVATE trace?" parameter should be "no".
To determine whether you are gathering an SNA Server/6000 link
station trace, use smit to view the SNA Server/6000 link station
configuration profile. The "Trace link?" parameter should be "no".
If you change any SNA Server/6000 configuration profiles, be sure
to "verify" and "update" them. Changes to link station profiles
require you to stop and start sna.
To determine whether you are gathering any PSF/MVS traces check
your JCL procedure and PRINTDEV statements. There are several
ways to activate a trace. I won't describe them here.
2) Several configuration parameters can affect performance. For
example, RU size, pacing, and link-level window.
Of these, the parameter that can have the greatest impact is
the link-level window. Whereas pacing is the flow control
mechanism for SNA's higher layers, the link-level window
provides flow control for the Data Link Control layer.
The MAXOUT parameter in VTAM or NCP definitions (I don't know
if your 3174 is local or remote) and the 3174 "W" item in
configuration item 941 indicate how many link-level frames
will be sent before waiting for a link-level acknowledgement
(Receive Ready). The "Receive window count (1-127)" in the
SNA DLC profile indicates how many link-level frames SNA
Server/6000 will receive before it sends an acknowledgement.
If the host side values are less than SNA Server's "receive
window count" performance can be extremely poor.
For example, if MAXOUT is 7 and the SNA Server/6000 "receive
window count" is 8 (its default value), the host side will
send 7 frames, then wait for a link-level acknowledgement.
SNA Server/6000 receives the 7 frames but waits for another
frame before it sends a link-level acknowledgement. Finally
after a second of waiting, SNA Server/6000 sends the link-level
acknowledgement.
The PSF Direct Network Configuration Guide describes this issue
more fully. It recommends that you set the "receive window
count" in the SNA Server/6000 DLC profile to a value less than
or equal to the host side values (MAXOUT and 3174 "W").
If you have any doubt, set the "receive window count" in the
SNA Server/6000 DLC profile to 1. This value will allow you
to achieve at least 90% of the theoretical optimum without
having to concern yourself with configuration consistency.
3) Finally, if your 3174 is remotely-attached, you should ensure
that the communication link between the host and the 3174 isn't
restricting overall throughput.
For example, assuming the 3174 is remotely connected via a
64 Kb/s facility (as is common in Europe), I'd estimate that
you could receive about 7 KBytes/sec of application data.
Your printer is a 3835, which prints roughly 90 impressions
per minute or 1.5 impressions/sec. So, the communication
facilities would only allow applications that average less
than 4.67 KBytes/page to print at rated speed.
Hopefully this information will help. If it does not, I suggest
you use a LAN trace tool like IBM DatagLANce or Network General
Sniffer to capture a minute of steady-state data flows. Don't
start the trace until the printer has been printing for several
minutes. Trace during the middle of a long job.
The trace should show a pattern. Is the host side slow in providing
data? Is the RISC side slow to provide a link-level acknowledgement
or pacing response? Etc.
If you're still stumped you could ask your communication specialist
for assistance or open a PSF/6000 PMR and we'll try to help. We'd
need all your configuration values (PSF/MVS, VTAM, NCP, 3174, SNA
Server/6000, PSF/6000) and a LAN trace as described above.
Closing.
Q:
We have a MAXOUT of 7 in the NCP and a receive window count of 127
on SNA Server. I don't know what the 3174 config is, as that was
subcontracted out and the information had not yet been returned.
However, based on what you have suggested it seems like we have the
wrong values here.
A:
Setting your SNA DLC "receive window count" to 127 would almost
certainly cause poor performance in your configuration. As you
noted, my previous response describes why.
In a remote 3174 configuration I'd set MAXOUT, 3174 941 "W"
(window), and the SNA DLC "receive window count" to the same
value. I don't think the host side can support more than 7.
If you have any uncertainty, set the SNA DLC "receive window
count" to 1. You'd still achieve near optimal performance,
especially if overall throughput is limited by a much slower
part of end-to-end communication such as a slow telecommunication
link.
Please refer to the PSF Direct Network Configuration Guide for
more information.
If you have a special interest in the intricacies of SNA, you
might get a LAN trace of a period of steady state data transfer.
I believe you'd see the host side send a fixed number of frames,
probably 7 if the 3174 941 W value is the same as the MAXOUT
setting. Then nearly a second of delay followed by a link-level
acknowledgement from SNA Server then 7 quick frames from the
host side, etc.
I hope this helps. Closing.
S e a r c h - k e y w o r d s:
AIX PSF/6000 PSF/AIX PSF DIRECT PERFORMANCE MAXOUT SNA 3174
infoprint lu6.2
WWQA: ITEM: RTA000090444 ITEM: RTA000090444
Dated: 07/1999 Category: XPSF6000
This HTML file was generated 2000/11/30~13:34:04
Comments or suggestions?
Contact us