Re: Real-Time Preemption and RCU

[Ingo Molnar <mingo@elte.hu>]

* Ingo Molnar <mingo@elte.hu> wrote:

> there's one detail on PREEMPT_RT though (which i think you noticed too). 
> 
> Priority inheritance handling can be done in a pretty straightforward
> way as long as no true read-side nesting is allowed for rwsems and
> rwlocks - i.e. there's only one owner of a lock at a time. So
> PREEMPT_RT restricts rwsem and rwlock concurrency: readers are
> writers, with the only exception that they are allowed to 'self-nest'.
> [...]

this does not affect read-side RCU, because read-side RCU can never
block a higher-prio thread. (as long as callback processing is pushed
into a separate kernel thread.)

so RCU will be pretty much the only mechanism (besides lock-free code)
that allows reader concurrency on PREEMPT_RT.

	Ingo