From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
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>
Subject: Re: [PATCH RFC tip/core/rcu 11/11] rcu: move TREE_RCU from softirq to kthread
Date: Wed, 2 Mar 2011 14:41:08 -0800 [thread overview]
Message-ID: <20110302224108.GA23194@linux.vnet.ibm.com> (raw)
In-Reply-To: <20110302000703.GK2218@linux.vnet.ibm.com>
On Tue, Mar 01, 2011 at 04:07:03PM -0800, Paul E. McKenney wrote:
> On Tue, Mar 01, 2011 at 03:38:11PM +0100, Peter Zijlstra wrote:
> > On Mon, 2011-02-28 at 16:13 -0800, Paul E. McKenney wrote:
[ . . . ]
> > 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.
>
> So as long as it is OK to call sched_setscheduler_nocheck() before
> the kthread is first awakened, we should be OK.
So the softlockup code kills me when I do it this way. Or can kill me.
>From what I can se the problem is that it might be the case that no one
needs a particular RCU kthread for some time. In addition, if the kthread
has not yet done the wait_event(), wake_up() won't know to wake it up.
The flag gets set, and all zero of the tasks blocked on the event's
queue are awakened, but the not-yet-awakened task still sleeps because
it has not yet done the wait_event().
So I am falling back to waking each thread up just after creation so
that they can be safely parked regardless of who needs which kthread at
what time in the future.
On the other hand, making these changes and testing them helped me find
and fix a number of subtle and not-so-subtle bugs in the TREE_RCU priority
boosting code, so I most certainly cannot argue with the outcome! ;-)
Thanx, Paul
next prev parent reply other threads:[~2011-03-02 22:41 UTC|newest]
Thread overview: 81+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-02-23 1:39 [PATCH tip/core/rcu 0/14] Preview of RCU patches for 2.6.39 Paul E. McKenney
2011-02-23 1:39 ` [PATCH RFC tip/core/rcu 01/11] rcu: call __rcu_read_unlock() in exit_rcu for tiny RCU Paul E. McKenney
2011-02-25 8:29 ` Lai Jiangshan
2011-02-25 19:40 ` Paul E. McKenney
2011-03-24 3:45 ` Lai Jiangshan
2011-03-24 13:07 ` Paul E. McKenney
2011-03-25 2:30 ` Paul E. McKenney
2011-02-23 1:39 ` [PATCH RFC tip/core/rcu 02/11] rcutorture: Get rid of duplicate sched.h include Paul E. McKenney
2011-02-23 1:39 ` [PATCH RFC tip/core/rcu 03/11] rcu: add documentation saying which RCU flavor to choose Paul E. McKenney
2011-02-23 1:39 ` [PATCH RFC tip/core/rcu 04/11] rcupdate: remove dead code Paul E. McKenney
2011-02-23 14:36 ` Mathieu Desnoyers
2011-02-23 1:39 ` [PATCH RFC tip/core/rcu 05/11] rcu: add comment saying why DEBUG_OBJECTS_RCU_HEAD depends on PREEMPT Paul E. McKenney
2011-02-23 3:23 ` Steven Rostedt
2011-02-23 13:59 ` Mathieu Desnoyers
[not found] ` <BLU0-SMTP615CB0BE0A2623EF62925096DB0@phx.gbl>
2011-02-23 14:11 ` Steven Rostedt
2011-02-23 14:37 ` Mathieu Desnoyers
2011-02-23 14:55 ` Steven Rostedt
2011-02-23 15:02 ` Mathieu Desnoyers
2011-02-23 15:13 ` [PATCH] debug rcu head support !PREEMPT config Mathieu Desnoyers
[not found] ` <BLU0-SMTP1519908E0ACAEE1384F71896DB0@phx.gbl>
2011-02-23 15:27 ` Steven Rostedt
2011-02-23 15:37 ` Mathieu Desnoyers
[not found] ` <BLU0-SMTP42770DC9BDE561B962274096DB0@phx.gbl>
2011-02-23 18:31 ` Paul E. McKenney
2011-02-23 18:40 ` Mathieu Desnoyers
[not found] ` <BLU0-SMTP900C4ABCF4001FBCB1594696DB0@phx.gbl>
2011-02-23 17:49 ` Paul E. McKenney
2011-02-23 1:39 ` [PATCH RFC tip/core/rcu 06/11] smp: Document transitivity for memory barriers Paul E. McKenney
2011-02-23 3:29 ` Steven Rostedt
2011-02-23 6:21 ` Lai Jiangshan
2011-02-23 15:14 ` Paul E. McKenney
2011-02-23 1:39 ` [PATCH RFC tip/core/rcu 07/11] rcu: Remove conditional compilation for RCU CPU stall warnings Paul E. McKenney
2011-02-23 1:39 ` [PATCH RFC tip/core/rcu 08/11] rcu: Decrease memory-barrier usage based on semi-formal proof Paul E. McKenney
2011-02-23 1:39 ` [PATCH RFC tip/core/rcu 09/11] rcu: merge TREE_PREEPT_RCU blocked_tasks[] lists Paul E. McKenney
2011-02-23 1:39 ` [PATCH RFC tip/core/rcu 10/11] rcu: Update documentation to reflect blocked_tasks[] merge Paul E. McKenney
2011-02-23 1:39 ` [PATCH RFC tip/core/rcu 11/11] rcu: move TREE_RCU from softirq to kthread Paul E. McKenney
2011-02-23 2:44 ` Frederic Weisbecker
2011-02-23 15:11 ` Paul E. McKenney
2011-02-23 3:09 ` Frederic Weisbecker
2011-02-23 15:12 ` Paul E. McKenney
2011-02-23 14:02 ` Mathieu Desnoyers
[not found] ` <BLU0-SMTP211F39903EDACD9B7E025C96DB0@phx.gbl>
2011-02-23 14:42 ` Steven Rostedt
2011-02-23 16:16 ` Frederic Weisbecker
2011-02-23 16:41 ` Steven Rostedt
2011-02-23 17:03 ` Mathieu Desnoyers
2011-02-23 17:14 ` Frederic Weisbecker
[not found] ` <BLU0-SMTP5642728A153E83B94895F896DB0@phx.gbl>
2011-02-23 17:30 ` Frederic Weisbecker
[not found] ` <BLU0-SMTP65F733B8D1D704C7EA1F8796DB0@phx.gbl>
2011-02-23 17:34 ` Christoph Lameter
2011-02-23 18:17 ` Steven Rostedt
2011-02-23 18:29 ` Christoph Lameter
2011-02-23 18:32 ` Steven Rostedt
2011-02-23 19:19 ` Christoph Lameter
2011-02-23 19:23 ` Peter Zijlstra
2011-02-23 19:35 ` Steven Rostedt
2011-02-23 19:40 ` Christoph Lameter
2011-02-23 20:15 ` Paul E. McKenney
2011-02-23 19:16 ` Paul E. McKenney
2011-02-23 19:24 ` Christoph Lameter
2011-02-23 20:45 ` Paul E. McKenney
2011-02-23 18:38 ` Mathieu Desnoyers
2011-02-23 18:27 ` Mathieu Desnoyers
2011-02-23 19:10 ` Paul E. McKenney
2011-02-23 19:22 ` Christoph Lameter
2011-02-23 19:39 ` Paul E. McKenney
2011-02-23 16:50 ` Frederic Weisbecker
2011-02-23 19:06 ` Paul E. McKenney
2011-02-23 19:13 ` Frederic Weisbecker
2011-02-23 20:41 ` Paul E. McKenney
[not found] ` <BLU0-SMTP57EE20F30B92B8763FD2FE96DB0@phx.gbl>
2011-02-23 18:52 ` Paul E. McKenney
2011-02-25 8:17 ` Lai Jiangshan
2011-02-25 20:32 ` Paul E. McKenney
2011-02-28 3:29 ` Lai Jiangshan
2011-02-28 9:47 ` Peter Zijlstra
2011-03-01 0:13 ` Paul E. McKenney
2011-03-01 14:38 ` Peter Zijlstra
2011-03-02 0:07 ` Paul E. McKenney
2011-03-02 22:41 ` Paul E. McKenney [this message]
2011-02-28 23:51 ` Paul E. McKenney
2011-03-02 1:52 ` Lai Jiangshan
2011-02-23 1:39 ` [PATCH RFC tip/core/rcu 12/14] rcu: priority boosting for TREE_PREEMPT_RCU Paul E. McKenney
2011-02-23 1:39 ` [PATCH RFC tip/core/rcu 13/14] rcu: eliminate unused boosting statistics Paul E. McKenney
2011-02-23 1:39 ` [PATCH RFC tip/core/rcu 14/14] rcu: Add boosting to TREE_PREEMPT_RCU tracing Paul E. McKenney
2011-02-23 3:07 ` Lai Jiangshan
2011-02-23 16:31 ` Paul E. McKenney
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