Subject: Re: [PATCH RFC tip/core/rcu 11/11] rcu: move TREE_RCU from softirq
 to kthread
From: Peter Zijlstra <peterz@infradead.org>
To: paulmck@linux.vnet.ibm.com
Cc: Lai Jiangshan <laijs@cn.fujitsu.com>, linux-kernel@vger.kernel.org,
        mingo@elte.hu, dipankar@in.ibm.com, akpm@linux-foundation.org,
        mathieu.desnoyers@polymtl.ca, josh@joshtriplett.org, niv@us.ibm.com,
        tglx@linutronix.de, rostedt@goodmis.org, Valdis.Kletnieks@vt.edu,
        dhowells@redhat.com, eric.dumazet@gmail.com, darren@dvhart.com,
        "Paul E. McKenney" <paul.mckenney@linaro.org>
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Date: Tue, 01 Mar 2011 15:38:11 +0100
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On Mon, 2011-02-28 at 16:13 -0800, Paul E. McKenney wrote:

> I am OK doing the sched_setscheduler_nocheck() in UP_PREPARE, correct?

Yeah, it should be perfectly fine to call that.

> Ah, there is the rub -- I am using wait_event(), so I need to wake up the
> kthread once before anyone uses it (or at least concurrently with anyone
> using it).  Which I can presumably do from the CPU_STARTING notifier.

Right, so your kthread is doing:

static int rcu_cpu_kthread()
{
  for (;;) {
    wait_event_interruptible();

    /* do stuff */

  }
  return 0;
}

Which means that all folks wanting to make use of this already need to
do a wakeup. So I don't see any reason to do that first wakeup from
CPU_STARTING.

wait_event() will only actually wait if the condition is false, in the
start-up case above it will find the condition true and fall right
through to do stuff.


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