lpt0 printer slows system response significantly

[Lowell Gilbert]

perryh at pluto.rain.com writes:

>> PID USERNAME  THR PRI NICE   SIZE    RES STATE    TIME   WCPU COMMAND
>>  18 root        1 -60 -179     0K     8K *Giant  15:09 77.05% irq7: lpt0
>>  11 root        1 171   52     0K     8K RUN     48.0H 11.13% idle
>
> The interrupt service for the parallel port is using over 3/4 of
> the CPU, and half of the rest is "idle".
>
> I take it this is a laser printer, which can consume bytes from the
> parallel port as fast as the processor can send them.  Top-of-head
> dump of ways to cut down on the interrupt traffic:
>
> * Get a DMA-capable parallel port (supposing such exist, and FreeBSD
>   supports them);
>
> * Move the printer to a network connection or dedicated print server;
>
> * Somehow tell the printer not to receive so quickly.

 * Change the printer port to polled mode.  ["lptcontrol -p"]
   With this kind of hardware, it may even speed up your printing as well.