Name
cytune — Tune Cyclades driver parameters
Synopsis
cytune [ −q [ −i interval ] ] [ [ −s value ] | [ −S value ] ] [ −g | G ] [ [ −t timeout ] | [ −T timeout ] ] tty [ tty... ]
DESCRIPTION
cytune
queries and modifies the interruption threshold for the
Cyclades driver. Each serial line on a Cyclades card has a
12-byte FIFO for input (and another 12-byte FIFO for output).
The "threshold" specifies how many input characters must be
present in the FIFO before an interruption is raised. When a
Cyclades tty is opened, this threshold is set to a default
value based on baud rate:
If the threshold is set too low, the large number of
interruptions can load the machine and decrease overall
system throughput. If the threshold is set too high, the FIFO
buffer can overflow, and characters will be lost. Slower
machines, however, may not be able to deal with the interrupt
load, and will require that the threshold be adjusted
upwards.
If the cyclades driver was compiled with ENABLE_MONITORING defined, the cytune
command can be used with the −q option to report interrupts over the
monitoring interval and characters transferred over the
monitoring interval. It will also report the state of the
FIFO. The maximum number of characters in the FIFO when an
interrupt occurred, the instantaneous count of characters in
the FIFO, and how many characters are now in the FIFO are
reported. This output might look like this:
/dev/cubC0: 830 ints, 9130 chars; fifo: 11 threshold,
11 max, 11 now
166.259866 interrupts/second, 1828.858521
characters/second
This output indicates that for this monitoring period, the
interrupts were always being handled within one character
time, because max
never rose above threshold. This is good, and
you can probably run this way, provided that a large number
of samples come out this way. You will lose characters if you
overrun the FIFO, as the Cyclades hardware does not seem to
support the RTS RS-232 signal line for hardware flow control
from the DCE to the DTE.
In query mode cytune will produce a summary
report when ended with a SIGINT or when the threshold or
timeout is changed.
There may be a responsiveness vs. throughput tradeoff. The
Cyclades card, at the higher speeds, is capable of putting a
very high interrupt load on the system. This will reduce the
amount of CPU time available for other tasks on your system.
However, the time it takes to respond to a single character
may be increased if you increase the threshold. This might be
noticed by monitoring ping(8) times on a SLIP link
controlled by a Cyclades card. If your SLIP link is generally
used for interactive work such as telnet(1), you may want to
leave the threshold low, so that characters are responded to
as quickly as possible. If your SLIP link is generally used
for file transfer, WWW, and the like, setting the FIFO to a
high value is likely to reduce the load on your system while
not significantly affecting throughput. Alternatively, see
the −t or −T options to adjust the time that the
cyclades waits before flushing its buffer. Units are 5ms.
If you are running a mouse on a Cyclades port, it is
likely that you would want to maintain the threshold and
timeout at a low value.
OPTIONS
−s
value-
Set the current threshold to value characters. Note
that if the tty
is not being held open by another process, the
threshold will be reset on the next open. Only values
between 1 and 12, inclusive, are permitted.
−t
value-
Set the current flush timeout to value units. Note that if
the tty is not
being held open by another process, the threshold will
be reset on the next open. Only values between 0 and
255, inclusive, are permitted. Setting value to zero forces the
default, currently 0x20 (160ms), but soon to be 0x02
(10ms). Units are 5 ms.
−g-
Get the current threshold and timeout.
−T
value-
Set the default flush timeout to value units. When the
tty is next
opened, this value will be used instead of the default.
If value is
zero, then the the value will default to 0x20 (160ms),
soon to be 0x02 (10ms).
−G-
Get the default threshold and flush timeout
values.
−q-
Gather statistics about the tty. The results are only
valid if the Cyclades driver has been compiled with
ENABLE_MONITORING
defined. This is probably not the default.
−i
interval-
Statistics will be gathered every interval seconds.
BUGS
If you run two copies of cytune at the same time to report
statistics about the same port, the 'ints', 'chars', and
'max' value will be reset and not reported correctly.
cytune should
prevent this, but does not.
FILES
/dev/ttyC[0-8]
/dev/cubC[0-8]
SEE ALSO
setserial(8)
cytune.8 --
Created: Sat Mar 4 17:44:53 1995 by faith@cs.unc.edu
Update: Sat Mar 4 18:22:24 1995 by faith@cs.unc.edu
Update: Sun Mar 5 06:40:12 1995 by njs@scifi.emi.net
Copyright 1995 Rickard E. Faith (faith@cs.unc.edu)
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