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

Nick Piggin
2004-09-14T22:58:11Z

Ingo Molnar wrote:
> * Nick Piggin <nickpiggin@yahoo.com.au> wrote:
>
>
>>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?
>
>
> two things:
>
> 1) none of the big distros enables CONFIG_PREEMPT in their kernels - not
> even SuSE. This is pretty telling.
>
> 2) 10 new cond_resched()'s are not precisely 'sprinkle everywhere'.
>

No, but I mean putting them right down into fastpaths like the vmscan
one, for example.

And if I remember correctly, you resorted to putting them into
might_sleep as well (but I haven't read the code for a while, maybe
you're now getting decent results without doing that).