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

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Message-Id: <1251098519.7538.139.camel@twins>
Date:	Mon, 24 Aug 2009 09:21:59 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josht@...ux.vnet.ibm.com,
	dvhltc@...ibm.com, niv@...ibm.com, tglx@...utronix.de,
	rostedt@...dmis.org
Subject: Re: [PATCH RFC -tip 0/4] v3 RCU cleanups and simplified
 preemptable RCU

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
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