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

[Nick Piggin]

Ingo Molnar wrote:
> * Nick Piggin <nickpiggin@xxxxxxxxxxxx> 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).
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