CP6100 I/O Process Programming Manual

Using CP6100: Managing Lines
Revising Line Parameters to Improve Performance
Among the parameters you define in SYSGEN--and possibly modify
with CMI--there are quite a few whose values affect the
| efficiency of a line. The System Management Manual for Tandem
NonStop Systems describes the parameters in detail. There are
also descriptions in the books that describe the protocols. The
next few pages discuss parameters only in terms of their effects
on performance.
If performance remains a problem even after you've finished
tuning, consider adding memory to increase available I/O pool
space. (Consider this move especially if applications get
frequent error 33's.)
CLBFRAMESIZE. This parameter defines the largest number of
bytes to be transferred between a 6101 controller and an LIU.
The value can range from 150 to 2048, and is 512 by default.
This parameter affects performance in two ways. First,
because frames to and from different lines are interleaved
on the same bus, the size of a frame represents a tradeoff
between CPU time--the more frames, the more processing--and
wait time--the larger the frames, the longer the average
wait for the bus.
MULTI. This parameter lets one instance of CP6100 control more
than one data communication line. Sometimes this strategy helps
conserve memory and dispatching overhead. On the other hand, all
the lines share the same 64K words of local pool; if the lines
are exceedingly busy, there might not be enough room for their
buffers. To find out whether the MULTI parameter helps your
configuration, take XRAY measurements including and excluding
MULTI.
MAXLOCALAREA. This parameter specifies the maximum read or write
count in a WRITEREAD call. The value can range from 1 to 32767,
and is 8000 (words) by default. This parameter, if its value is
too large, can impede performance because applications must wait
for large buffers to become available.
October 1985
3-32