Re: Sub jiffy delay?

From: Steven Rostedt
Date: Wed Nov 23 2005 - 16:20:44 EST

On Wed, 2005-11-23 at 15:39 -0500, Rick Niles wrote:
> I need to service a piece of hardware about every 400-500
> microseconds, but I really don't want to change the value of HZ, which
> in my version of the 2.6 kernel is 1000. The hardware doesn't have an
> interrupt so the nasty hack I've been doing is to service the hardware
> repeatedly in a loop for about 600 microseconds by watching the
> do_gettimeofday(), set a timer for the next jiffy and repeat. This leaves less than 400 microseconds / millisecond for the kernel and anything else on the system to run.
> Obviously, this sucks, but it does work. I am working with the
> hardware guy to add an interrupt to the hardware. However, I don't
> want every user of the hardware without the interrupt to have to
> rebuild the kernel with a different value of HZ. So does anyone have
> any better ideas on what I can do?

Have you looked at Thomas Gleixner's ktimer/HRT patches. It gives you a
way to set a timer to go off within a jiffy.

-- Steve

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