Re: A better interface, perhaps: a timed signal flag

From: Steven Rostedt
Date: Fri Jul 28 2006 - 12:43:27 EST

On Fri, 2006-07-28 at 17:41 +0100, Alan Cox wrote:
> Ar Gwe, 2006-07-28 am 10:52 -0400, ysgrifennodd Theodore Tso:
> > Good point, and limiting this facility to one such timeout per
> > task_struct seems like a reasonable restriction.
> Why is this any better than using a thread or signal handler ? From the
> implementation side its certainly horrible - we will be trying to write
> user pages from an IRQ event. Far better to let the existing thread code
> deal with it.

If the user page is special, in that it is really a kernel page mapped
to userspace. The implementation on making sure it doesn't disappear on
the interrupt isn't that difficult.

But for real-time applications, the signal handling has a huge latency.
Where as what Theodore wants to do is very light weight. ie. have a
high prio task doing smaller tasks until a specific time that tells it
to stop. Having a signal, would create the latency on having that task

These little requests make sense really only in the real-time space.
The normal uses can get by with signals. But I will say, the normal
uses for computing these days are starting to want the real-time
powers. :)

-- Steve

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