cytune — Tune Cyclades driver parameters
cytune
[ −q
[ −i
interval ] ] [ [ −s
value ] | [ −S
value ] ] [ −g
| G ] [ [ −t
timeout ] | [ −T
timeout ] ] tty [ tty... ]
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:
Baud Threshold 50-4800 10 9600 8 19200 4 38400 2 57600-150000 1
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.
−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.
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.
setserial(8)
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