lpt0 printer slows system response significantly

[Ted Mittelstaedt]

You can also get a faster CPU, more cycles available for servicing
interrupts.

Ted

----- Original Message ----- 
From: <perryh at pluto.rain.com>
To: <mexas at bristol.ac.uk>
Cc: <freebsd-questions at freebsd.org>
Sent: Wednesday, November 01, 2006 12:02 AM
Subject: Re: lpt0 printer slows system response significantly


> > 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.
>
> Alternatively, one possible way to handle that sort of interrupt
> load without bogging down is to get a second CPU and run SMP, so
> you've still got a CPU available for tasks when one is swamped
> with interrupt traffic.
>
> The other thing that *might* help some is more RAM, if it happens
> that the idle time is caused by page wait due to the set of active
> threads needing more RAM than you have, but this will at best get
> your tasks up from 1/9 of the CPU to 2/9.
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