Re: [PATCH 26/30] sched: handle preempt=voluntary under PREEMPT_AUTO

[Paul E. McKenney]

On Mon, Mar 11, 2024 at 01:23:09PM -0700, Linus Torvalds wrote:
> On Mon, 11 Mar 2024 at 13:10, Ankur Arora <ankur.a.arora@xxxxxxxxxx> wrote:
> >
> > Ah, I see your point. Basically, keep the lazy semantics but -- in
> > addition -- also provide the ability to dynamically toggle
> > cond_resched(), might_reshed() as a feature to help move this along
> > further.
> 
> Please, let's not make up any random hypotheticals.
> 
> Honestly, if we ever hit the hypothetical scenario that Paul outlined, let's
> 
>  (a) deal with it THEN, when we actually know what the situation is
> 
>  (b) learn and document what it is that actually causes the odd behavior
> 
> IOW, instead of assuming that some "cond_resched()" case would even be
> the right thing to do, maybe there are other issues going on?  Let's
> not paper over them by keeping some hack around - and *if* some
> cond_resched() model is actually the right model in some individual
> place, let's make it the rule that *when* we hit that case, we
> document it.
> 
> And we should absolutely not have some hypothetical case keep us from
> just doing the right thing and getting rid of the existing
> cond_resched().
> 
> Because any potential future case is *not* going to be the same
> cond_resched() that the current case is anyway. It is going to have
> some very different cause.

Fair enough, and that approach just means that we will be reaching out
to Ankur and Thomas sooner rather than later if something goes sideways
latency-wise.  ;-)

							Thanx, Paul