On Sat, 27 May 2000, mark wrote:
> > 1. recompile your kernel with HZ defined to 1000 or 2000
> As a matter of interest what exactly does this parameter do? I don't
It is the frequency of timer interrupt, which in turn reschedules tasks.
The minimum sleep time (usleep()) is two times the tick.
> really do much with the kernel sources. I assume it somehow hardware
> dependent as to the value you can realistically set this? I can't imagin
I was running with no problems at 1000. You will need to recompile all
modules with that in place! My soft RT program in user space was running
fine with that, missing ticks only on very heavy disk activity.
> its how long the kernel take until is context switches. The current
> setting is 100, it would be dog slow! :)
This is the way Linus wanted it. See KURT/ microsecond resolution patch for
improvement. May be 2.4 kernel will be better.
> However I've read some other documents as realise that without
> semi-rewritting the NIC driver so it works in the RT domain the project
> would be rarther pointless. However I did set a port of the tulip.c
> driver. Could use that.
Yes. Then you should split your application in the kernel RT part taking
prepared frames (complete with ethernet header) from some buffer (I would
recommend some structure placed in mbuff (my shared memory implemementation))
and sending them to that RT net driver (you can than achieve jitter as
low as 1 microsecond if you call your function 20-30 us early and then wait
on TSC to reach the proper time).
Best regards,
--
Tomek
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