linux-kernel - Re: [PATCH RFC tip/core/rcu 11/11] rcu: move TREE

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Message-ID: <1298990291.5226.870.camel@laptop>
Date:	Tue, 01 Mar 2011 15:38:11 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	paulmck@...ux.vnet.ibm.com
Cc:	Lai Jiangshan <laijs@...fujitsu.com>, linux-kernel@...r.kernel.org,
	mingo@...e.hu, dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, rostedt@...dmis.org,
	Valdis.Kletnieks@...edu, dhowells@...hat.com,
	eric.dumazet@...il.com, darren@...art.com,
	"Paul E. McKenney" <paul.mckenney@...aro.org>
Subject: Re: [PATCH RFC tip/core/rcu 11/11] rcu: move TREE_RCU from softirq
 to kthread

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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