Re: [patch] sched: fix scheduling latencies for !PREEMPT kernels

Nick Piggin
2004-09-14T13:37:12Z

Ingo Molnar wrote:
> * Nick Piggin <nickpiggin@yahoo.com.au> wrote:
>
>
>>Could these ones go up a level? We break down scanning into 32 page
>>chunks, so I don't think it needs to be checked every page.
>
>
> not really - we can occasionally get into high latencies even with a
> single page - if a single page is mapped by alot of processes.
>

So doing it in the loop doesn't really give you a deterministic
maximum latency if somebody is out to cause trouble, does it?

OTOH, I guess libc or some shared memory segment may be mapped
into a lot of processes even on RT applictions.

Another thing, I don't mean this to sound like a rhetorical question,
but if we have a preemptible kernel, why is it a good idea to sprinkle
cond_rescheds everywhere? Isn't this now the worst of both worlds?
Why would someone who really cares about latency not enable preempt?