[Lcdproc] LCDd 0.5.1 eating almost alll CPU on Debian Etch

[Stefan Herdler]

Hi,
Mattia Jona-Lasinio wrote:
> Hi all,
>
> I'm the maintainer of the LCD-Linux project which is a kernel driver 
> for the
> HD44780 controller connected to the parallel port.
> I experience the same problem as you report here: programs using
> LCD-Linux eat a
> lot of cpu time. This happened since I moved to a distribution with a
> 2.6 Linux
> kernel. With the 2.4 kernel the cpu load was almost unreadable.
My experiences had been quiet similar. On my kernel 2.4 (HZ 1000) system 
everything was working with moderate CPU usage while users with 2.6 
kernel have been reporting massive problems.
> Therefore I don't think it is a matter of busy waiting loops but rather a
> problem of HZ value in the kernel as Stefan suggested. 
Changing the Hz value I was able to switch between the 2 extremes,
High CPU-load and fast refreshing and low CPU-load and unusable slow (1 
char/sec) refresh.
I was using the predefined timing_uPause() function compiled to use 
nanosleep().
It looks like nanosleep() switches between sleep- and busy-loop-timing, 
but I haven't found helpful informations about that.

So I decided to use port-I/O-timing reading the BUSY-line of the display.
It isn't the the most effective way, I think, but it seems to work 
reliable with moderate CPU-load on all tested systems.

I recently took a look into the conf-file of  Graph-LCD 
<http://developer.berlios.de/project/showfiles.php?group_id=356>, they 
recommend to use timing with "gettimeofday" for the 2.6 kernels.
Perhaps it helps.
** <http://dict.leo.org/ende?lp=ende&p=/gQPU.&search=recommend>
> Can someone try
> a kernel
> compiled with the old 100 Hz value? Most kernels included in 
> distributions are
> compiled with a HZ value of 1000 to take advantage of the new 2.6 Linux
> scheduler and to have a finer grained time for processes.
I currently don't have a running HD44780 display, sorry.
> My tests are done on an Athlon 2800+ CPU with 1Gb of RAM. I think this
> is quite
> a fast machine to handle LCD stuff.
>
> Bye,
>
> Mattia
>
>
Stefan