Re: [2.4.17/18pre] VM and swap - it's really unusable

[Roger Larsson]

On Tuesdayen den 8 January 2002 21.13, Alan Cox wrote:
> > low-latency kernel".  Now, IF we can come to this decision, then
> > internal preemption is the way to do it.  But it affects ALL kernel
>
> The pre-empt patches just make things much much harder to debug. They
> remove some of the predictability and the normal call chain following
> goes out of the window because you end up seeing crashes in a thread with
> no idea what ran the microsecond before
>
> Some of that happens now but this makes it vastly worse.
>
> The low latency patches don't change the basic predictability and
> debuggability but allow you to hit a 1mS pre-empt target for the general
> case.
>

Yes, it does make things much much harder to debug - but:
* If you get a problem on a preemtive UP kernel, it is likely to be a problem
  on a SMP too - and those are hard to debug aswell. But the positive aspect
  is that you get more people that can do the debugging... :-)
  (One CPU gets delayed with handling a IRQ the other runs into the critical
   section)
* It is optional at compile time.
   And could even be made run time optional / CPU ! Just set a too big value
   on the counter and it will never reschedule...

/RogerL

-- 
Roger Larsson
Skellefteċ
Sweden