Re: [PATCH RFC -tip 0/4] v3 RCU cleanups and simplified preemptable RCU

[Peter Zijlstra <peterz@infradead.org>]

On Sat, 2009-08-22 at 13:52 -0700, Paul E. McKenney wrote:
> 
> o       Rename variables and functions so that RCU-sched is an
>         underlying definition, along with RCU-bh and (when so
>         configured) RCU-preempt.  RCU then maps to either RCU-sched
>         or RCU-preempt, depending on configuration.

Nice, but we're not quite there yet it seems, since RCU-preempt isn't
available outside of TREE_PREEMPT_RCU afaiks.

That is, I'm still hoping for the day that generic code can do:

  rcu_preempt_read_lock();


  call_rcu_preempt(&my_rcu_thing);
  rcu_preempt_read_unlock();

And have it work like expected, this would, I think, remove much of the
need for SRCU.


The thing I've talked about earlier is an extension of this where you
can create multiple RCU domains along the lines of:

  struct rcu_preempt_domain my_domain;

  rcu_preempt_init(&my_domain);


and

  rcu_preempt_read_lock(&my_domain);

  call_rcu_preempt(&my_domain, &my_rcu_head);
  rcu_preempt_read_unlock(&my_domain);


Which would allow you to create smaller RCU domains for when you want
faster grace periods due to less interference of other rcu users.


Anyway, enough rambling, the patch-set does look very nice, and if time
permits I'll try and go through the preempt-tree-rcu thing.

Thanks