* Ingo Molnar <[EMAIL PROTECTED]> wrote: > > * Paul E. McKenney <[EMAIL PROTECTED]> wrote: > > > I have tested this approach, but in user-level scaffolding. All of > > these implementations should therefore be regarded with great > > suspicion: untested, probably don't even compile. Besides which, I > > certainly can't claim to fully understand the real-time preempt patch, > > so I am bound to have gotten something wrong somewhere. [...] > > you dont even have to consider the -RT patchset: if the scheme allows > forced preemption of read-side RCU sections on current upstream > CONFIG_PREEMPT, then it's perfect for PREEMPT_RT too.
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'. I.e. things like: read_lock(&rwlock); ... read_lock(&rwlock); are still legal. (it's also done quite often.) (it is virtually impossible to implement priority inheritance for true multi-reader locks in any sane way: i've done it initially and it sucks very much. It also fundamentally increases the 'lock-dependent' worst-case latencies - imagine 4 readers having to finish first if a higher-prio writer comes along. It's insane.) Ingo - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/