Re: [tip: sched/core] sched: Fix performance regression introduced by mm_cid

[Sebastian Andrzej Siewior]

On 2023-06-23 00:35:29 [-0700], John Johansen wrote:
> > 
> iirc the difference with the earlier version, is in the put case. Where in
> the earlier version, if there was lock contention the buffer would always
> get pushed onto the percpu list. With some debug patches on top we
> saw some degenerate cases where this would result in percpu lists that
> had excessive buffers on them.
> 
> So this version added a condition to force putting the buffer back
> in to the global pool if the percpu list already has 2 buffers
> cached on it.

So none of the versions perform memory allocation/ deallocation in a
preempt disabled section so it is fine from PREEMPT_RT point of view.

Sebastian