Re: [PATCH v2 7/9] sched: define TIF_ALLOW_RESCHED

Paul E. McKenney
2023-10-18T23:26:05Z

On Thu, Oct 19, 2023 at 12:53:05AM +0200, Thomas Gleixner wrote:
> On Wed, Oct 18 2023 at 10:51, Paul E. McKenney wrote:
> > On Wed, Oct 18, 2023 at 05:09:46AM -0700, Ankur Arora wrote:
>
> Can you folks please trim your replies. It's annoying to scroll
> through hundreds of quoted lines to figure out that nothing is there.
>
> >> This probably allows for more configuration flexibility across archs?
> >> Would allow for TREE_RCU=y, for instance. That said, so far I've only
> >> been working with PREEMPT_RCU=y.)
> >
> > Then this is a bug that needs to be fixed. We need a way to make
> > RCU readers non-preemptible.
>
> Why?

So that we don't get tail latencies from preempted RCU readers that
result in memory-usage spikes on systems that have good and sufficient
quantities of memory, but which do not have enough memory to tolerate
readers being preempted.

Thanx, Paul