From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Joe Korty <joe.korty@ccur.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>,
"mathieu.desnoyers@efficios.com" <mathieu.desnoyers@efficios.com>,
"dhowells@redhat.com" <dhowells@redhat.com>,
"loic.minier@linaro.org" <loic.minier@linaro.org>,
"dhaval.giani@gmail.com" <dhaval.giani@gmail.com>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"peterz@infradead.org" <peterz@infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"josh@joshtriplett.org" <josh@joshtriplett.org>,
Jim Houston <jim.houston@comcast.net>
Subject: Re: [PATCH] a local-timer-free version of RCU
Date: Mon, 8 Nov 2010 11:50:19 -0800 [thread overview]
Message-ID: <20101108195019.GD4032@linux.vnet.ibm.com> (raw)
In-Reply-To: <20101108151829.GB8996@tsunami.ccur.com>
On Mon, Nov 08, 2010 at 10:18:29AM -0500, Joe Korty wrote:
> On Mon, Nov 08, 2010 at 10:06:47AM -0500, Frederic Weisbecker wrote:
> > On Sat, Nov 06, 2010 at 12:28:12PM -0700, Paul E. McKenney wrote:
> >> OK, so your approach treats preempt_disable code sequences as RCU
> >> read-side critical sections by relying on the fact that the per-CPU
> >> ->krcud task cannot run until such code sequences complete, correct?
> >>
> >> This seems to require that each CPU's ->krcud task be awakened at
> >> least once per grace period, but I might well be missing something.
> >
> > I understood it differently, but I might also be wrong as well. krcud
> > executes the callbacks, but it is only woken up for CPUs that want to
> > execute callbacks, not for those that only signal a quiescent state,
> > which is only determined in two ways through rcu_poll_other_cpus():
> >
> > - if the CPU is in an rcu_read_lock() critical section, it has the
> > IN_RCU_READ_LOCK flag. If so then we set up its DO_RCU_COMPLETION flag so
> > that it signals its quiescent state on rcu_read_unlock().
> >
> > - otherwise it's in a quiescent state.
> >
> > This works for rcu and rcu bh critical sections.
> > But this works in rcu sched critical sections only if rcu_read_lock_sched() has
> > been called explicitly, otherwise that doesn't work (in preempt_disable(),
> > local_irq_save(), etc...). I think this is what is not complete when
> > Joe said it's not yet a complete rcu implementation.
> >
> > This is also the part that scaries me most :)
>
> Mostly, I meant that the new RCU API interfaces that have come into
> existance since 2004 were only hastily wrapped or NOPed by me to get
> things going.
Ah, understood.
> Jim's method only works with explicit rcu_read_lock..unlock sequences,
> implicit sequences via preempt_disable..enable and the like are not
> handled. I had thought all such sequences were converted to rcu_read_lock
> but maybe that is not yet correct.
Not yet, unfortunately. Having them all marked, for lockdep if nothing
else, could be a big benefit.
> Jim will have to comment on the full history. He is incommunicado
> at the moment; hopefully he will be able to participate sometime in
> the next few days.
Sounds good!
Thanx, Paul
next prev parent reply other threads:[~2010-11-08 19:50 UTC|newest]
Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-11-04 23:21 dyntick-hpc and RCU Paul E. McKenney
2010-11-05 5:27 ` Frederic Weisbecker
2010-11-05 5:38 ` Frederic Weisbecker
2010-11-05 15:06 ` Paul E. McKenney
2010-11-05 20:06 ` Dhaval Giani
2010-11-05 15:04 ` Paul E. McKenney
2010-11-08 14:10 ` Frederic Weisbecker
2010-11-05 21:00 ` [PATCH] a local-timer-free version of RCU Joe Korty
2010-11-06 19:28 ` Paul E. McKenney
2010-11-06 19:34 ` Mathieu Desnoyers
2010-11-06 19:42 ` Mathieu Desnoyers
2010-11-06 19:44 ` Paul E. McKenney
2010-11-08 2:11 ` Udo A. Steinberg
2010-11-08 2:19 ` Udo A. Steinberg
2010-11-08 2:54 ` Paul E. McKenney
2010-11-08 15:32 ` Frederic Weisbecker
2010-11-08 19:38 ` Paul E. McKenney
2010-11-08 20:40 ` Frederic Weisbecker
2010-11-10 18:08 ` Paul E. McKenney
2010-11-08 15:06 ` Frederic Weisbecker
2010-11-08 15:18 ` Joe Korty
2010-11-08 19:50 ` Paul E. McKenney [this message]
2010-11-08 19:49 ` Paul E. McKenney
2010-11-08 20:51 ` Frederic Weisbecker
2010-11-06 20:03 ` Mathieu Desnoyers
2010-11-09 9:22 ` Lai Jiangshan
2010-11-10 15:54 ` Frederic Weisbecker
2010-11-10 17:31 ` Peter Zijlstra
2010-11-10 17:45 ` Frederic Weisbecker
2010-11-11 4:19 ` Paul E. McKenney
2010-11-13 22:30 ` Frederic Weisbecker
2010-11-16 1:28 ` Paul E. McKenney
2010-11-16 13:52 ` Frederic Weisbecker
2010-11-16 15:51 ` Paul E. McKenney
2010-11-17 0:52 ` Frederic Weisbecker
2010-11-17 1:25 ` Paul E. McKenney
2011-03-07 20:31 ` [PATCH] An RCU for SMP with a single CPU garbage collector Joe Korty
[not found] ` <20110307210157.GG3104@linux.vnet.ibm.com>
2011-03-07 21:16 ` Joe Korty
2011-03-07 21:33 ` Joe Korty
2011-03-07 22:51 ` Joe Korty
2011-03-08 9:07 ` Paul E. McKenney
2011-03-08 15:57 ` Joe Korty
2011-03-08 22:53 ` Joe Korty
2011-03-10 0:30 ` Paul E. McKenney
2011-03-10 0:28 ` Paul E. McKenney
2011-03-09 22:29 ` Frederic Weisbecker
2011-03-09 22:15 ` [PATCH 2/4] jrcu: tap rcu_read_unlock Joe Korty
2011-03-10 0:34 ` Paul E. McKenney
2011-03-10 19:50 ` JRCU Theory of Operation Joe Korty
2011-03-12 14:36 ` Paul E. McKenney
2011-03-13 0:43 ` Joe Korty
2011-03-13 5:56 ` Paul E. McKenney
2011-03-13 23:53 ` Joe Korty
2011-03-14 0:50 ` Paul E. McKenney
2011-03-14 0:55 ` Josh Triplett
2011-03-09 22:16 ` [PATCH 3/4] jrcu: tap might_resched() Joe Korty
2011-03-09 22:17 ` [PATCH 4/4] jrcu: add new stat to /sys/kernel/debug/rcu/rcudata Joe Korty
2011-03-09 22:19 ` [PATCH 1/4] jrcu: remove preempt_enable() tap [resend] Joe Korty
2011-03-12 14:36 ` [PATCH] An RCU for SMP with a single CPU garbage collector Paul E. McKenney
2011-03-13 1:25 ` Joe Korty
2011-03-13 6:09 ` Paul E. McKenney
[not found] <757455806.950179.1289232791283.JavaMail.root@sz0076a.westchester.pa.mail.comcast.net>
2010-11-08 16:15 ` [PATCH] a local-timer-free version of RCU houston.jim
2010-11-08 19:52 ` Paul E. McKenney
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