From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Christoph Lameter <cl@linux.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
Frederic Weisbecker <fweisbec@gmail.com>,
linux-kernel@vger.kernel.org, mingo@elte.hu,
laijs@cn.fujitsu.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, josh@joshtriplett.org, niv@us.ibm.com,
tglx@linutronix.de, peterz@infradead.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, 23 Feb 2011 11:16:58 -0800 [thread overview]
Message-ID: <20110223191658.GV2163@linux.vnet.ibm.com> (raw)
In-Reply-To: <alpine.DEB.2.00.1102231225330.3906@router.home>
On Wed, Feb 23, 2011 at 12:29:59PM -0600, Christoph Lameter wrote:
> On Wed, 23 Feb 2011, Steven Rostedt wrote:
>
> > On Wed, 2011-02-23 at 11:34 -0600, Christoph Lameter wrote:
> >
> > > > > True, but we could also argue that the multiple checks for being preempt
> > > > > can also be an issue.
> > > >
> > > > At least on x86 preemption don't actually need to be disabled: selection
> > > > of the right per-cpu memory location is done atomically with the rest of
> > > > the instruction by the segment selector.
> > >
> > > Right.
> >
> > But a test still needs to be made. Because three access of this_cpu_*()
> > that gets preempted and scheduled on another CPU can access a different
> > CPU var for each access. This does not matter how atomic the
> > this_cpu_*() code is.
>
> Right if the kthread context can be rescheduled then either preemption
> needs to be disabled to guarantee that all three access the same per cpu
> area data or the code needs to be changed in such a way that a this_cpu
> RMW instructions can do the mods in one go.
Reschedules can happen in this case due to CPU hotplug events. :-(
Thanx, Paul
next prev parent reply other threads:[~2011-02-23 19:17 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 [this message]
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
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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