lpt0 printer slows system response significantly

[Anton Shterenlikht]

	Hello

	I have a printer attached to a parallel port on an old
Compaq Armada 1700 laptop. When I print large (> 100k) documents
the system responds very slow (1-3sec) to keyboard strokes or
mouse moves. I wonder if I can lower the priority of printing.

	The details:
$dmesg

[skip]

FreeBSD 6.0-RELEASE #1: Thu Sep 14 10:40:41 BST 2006
Timecounter "i8254" frequency 1193182 Hz quality 0
CPU: Pentium II/Pentium II Xeon/Celeron (233.34-MHz 686-class CPU)
  Origin = "GenuineIntel"  Id = 0x652  Stepping = 2
  Features=0x183f9ff<FPU,VME,DE,PSE,TSC,MSR,PAE,MCE,CX8,SEP,MTRR,PGE,MCA,CMOV,PAT,PSE36,MMX,FXSR>
real memory  = 167772160 (160 MB)
avail memory = 158879744 (151 MB)

[skip]

lpt0: <Printer> on ppbus0
lpt0: Interrupt-driven port
ppi0: <Parallel I/O> on ppbus0


	Two typical outputs from top taken during printing:

last pid: 12387;  load averages:  0.75,  0.44,  0.23  up 2+01:16:32    10:48:06
89 processes:  2 running, 63 sleeping, 23 waiting, 1 lock

Mem: 81M Active, 24M Inact, 37M Wired, 6940K Cache, 25M Buf, 3868K Free
Swap: 128M Total, 108K Used, 128M Free


  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
12269 daemon      1  -8    0 10996K  8908K pipewr   0:27  6.15% gs
  485 root        1  96    0 18064K 16668K select   6:30  0.00% Xorg
   28 root        1 -32 -151     0K     8K WAIT     5:05  0.00% swi4: clock sio

	and

last pid: 12388;  load averages:  0.75,  0.44,  0.23  up 2+01:16:34    10:48:08
89 processes:  3 running, 62 sleeping, 24 waiting

Mem: 81M Active, 24M Inact, 37M Wired, 6940K Cache, 25M Buf, 3868K Free
Swap: 128M Total, 108K Used, 128M Free


  PID USERNAME  THR PRI NICE   SIZE    RES STATE    TIME   WCPU COMMAND
   18 root        1 -60 -179     0K     8K WAIT    15:10 77.34% irq7: ppc0
   11 root        1 171   52     0K     8K RUN     48.0H 10.89% idle
12269 daemon      1  99    0 10996K  8908K RUN      0:28  5.57% gs
   40 root        1 171   52     0K     8K pgzero   0:35  0.15% pagezero
12270 daemon      1  -8    0  1184K   580K piperd   0:01  0.05% cat
  485 root        1  96    0 18064K 16668K select   6:30  0.00% Xorg
   28 root        1 -32 -151     0K     8K WAIT     5:05  0.00% swi4: clock sio

	In the user manual I found about vm.swap_idle_enables kernel
variable. Is that something I should try?

thanks
anton