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From: "Paul E. McKenney" <paulmck@linux.ibm.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org,
	mingo@kernel.org, jiangshanlai@gmail.com, dipankar@in.ibm.com,
	akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
	josh@joshtriplett.org, tglx@linutronix.de, rostedt@goodmis.org,
	dhowells@redhat.com, edumazet@google.com, fweisbec@gmail.com,
	oleg@redhat.com, joel@joelfernandes.org
Subject: Re: [PATCH RFC tip/core/rcu 01/14] rcu/nocb: Atomic ->len field in rcu_segcblist structure
Date: Sun, 4 Aug 2019 11:42:46 -0700	[thread overview]
Message-ID: <20190804184246.GD28441@linux.ibm.com> (raw)
In-Reply-To: <20190804145051.GG2349@hirez.programming.kicks-ass.net>

On Sun, Aug 04, 2019 at 04:50:51PM +0200, Peter Zijlstra wrote:
> On Fri, Aug 02, 2019 at 08:14:48AM -0700, Paul E. McKenney wrote:
> > +/*
> > + * Exchange the numeric length of the specified rcu_segcblist structure
> > + * with the specified value.  This can cause the ->len field to disagree
> > + * with the actual number of callbacks on the structure.  This exchange is
> > + * fully ordered with respect to the callers accesses both before and after.
> > + */
> > +long rcu_segcblist_xchg_len(struct rcu_segcblist *rsclp, long v)
> > +{
> > +#ifdef CONFIG_RCU_NOCB_CPU
> > +	return atomic_long_xchg(&rsclp->len, v);
> > +#else
> > +	long ret = rsclp->len;
> > +
> > +	smp_mb(); /* Up to the caller! */
> > +	WRITE_ONCE(rsclp->len, v);
> > +	smp_mb(); /* Up to the caller! */
> > +	return ret;
> > +#endif
> > +}
> 
> That one's weird; for matching semantics the load needs to be between
> the memory barriers.

This is to match the concurrent version, which uses atomic_xchg().

							Thanx, Paul

  parent reply	other threads:[~2019-08-04 18:43 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-08-02 15:14 [PATCH tip/core/rcu 0/14] No-CBs bypass addition for v5.4 Paul E. McKenney
2019-08-02 15:14 ` [PATCH RFC tip/core/rcu 01/14] rcu/nocb: Atomic ->len field in rcu_segcblist structure Paul E. McKenney
2019-08-04 14:50   ` Peter Zijlstra
2019-08-04 14:52     ` Peter Zijlstra
2019-08-04 18:45       ` Paul E. McKenney
2019-08-04 18:42     ` Paul E. McKenney [this message]
2019-08-02 15:14 ` [PATCH RFC tip/core/rcu 02/14] rcu/nocb: Add bypass callback queueing Paul E. McKenney
2019-08-07  0:03   ` Joel Fernandes
2019-08-07  0:16     ` Joel Fernandes
2019-08-07  0:35     ` Paul E. McKenney
2019-08-07  0:40       ` Steven Rostedt
2019-08-07  1:17         ` Paul E. McKenney
2019-08-07  1:24           ` Steven Rostedt
2019-08-07  3:47             ` Paul E. McKenney
2019-08-02 15:14 ` [PATCH RFC tip/core/rcu 03/14] rcu/nocb: EXP Check use and usefulness of ->nocb_lock_contended Paul E. McKenney
2019-08-02 15:14 ` [PATCH RFC tip/core/rcu 04/14] rcu/nocb: Print no-CBs diagnostics when rcutorture writer unduly delayed Paul E. McKenney
2019-08-02 15:14 ` [PATCH RFC tip/core/rcu 05/14] rcu/nocb: Avoid synchronous wakeup in __call_rcu_nocb_wake() Paul E. McKenney
2019-08-02 15:14 ` [PATCH RFC tip/core/rcu 06/14] rcu/nocb: Advance CBs after merge in rcutree_migrate_callbacks() Paul E. McKenney
2019-08-02 15:14 ` [PATCH RFC tip/core/rcu 07/14] rcu/nocb: Reduce nocb_cb_wait() leaf rcu_node ->lock contention Paul E. McKenney
2019-08-02 15:14 ` [PATCH RFC tip/core/rcu 08/14] rcu/nocb: Reduce __call_rcu_nocb_wake() " Paul E. McKenney
2019-08-02 15:14 ` [PATCH RFC tip/core/rcu 09/14] rcu/nocb: Don't wake no-CBs GP kthread if timer posted under overload Paul E. McKenney
2019-08-02 15:14 ` [PATCH RFC tip/core/rcu 10/14] rcu: Allow rcu_do_batch() to dynamically adjust batch sizes Paul E. McKenney
2019-08-02 15:14 ` [PATCH RFC tip/core/rcu 11/14] EXP nohz: Add TICK_DEP_BIT_RCU Paul E. McKenney
2019-08-02 15:14 ` [PATCH RFC tip/core/rcu 12/14] rcu/nohz: Force on tick when invoking lots of callbacks Paul E. McKenney
2019-08-02 15:15 ` [PATCH RFC tip/core/rcu 13/14] rcutorture: Force on tick for readers and callback flooders Paul E. McKenney
2019-08-02 15:15 ` [PATCH RFC tip/core/rcu 14/14] rcu/nohz: Make multi_cpu_stop() enable tick on all online CPUs Paul E. McKenney
2019-08-04 14:43   ` Peter Zijlstra
2019-08-04 14:48     ` Peter Zijlstra
2019-08-04 18:41       ` Paul E. McKenney
2019-08-04 20:24         ` Paul E. McKenney
2019-08-05  4:19           ` Paul E. McKenney
2019-08-05  8:07             ` Peter Zijlstra
2019-08-05 14:47               ` Paul E. McKenney
2019-08-05  8:05         ` Peter Zijlstra
2019-08-05 14:54           ` Paul E. McKenney
2019-08-05 15:50             ` Peter Zijlstra
2019-08-05 17:48               ` Paul E. McKenney
2019-08-06 18:08                 ` Paul E. McKenney
2019-08-07 21:41                   ` Paul E. McKenney
2019-08-08 20:35                     ` Paul E. McKenney
2019-08-08 21:30                       ` Paul E. McKenney
2019-08-09 16:51                         ` Paul E. McKenney
2019-08-09 18:07                           ` Joel Fernandes
2019-08-09 18:39                             ` Paul E. McKenney
2019-08-12 21:02   ` Frederic Weisbecker
2019-08-12 23:23     ` Paul E. McKenney
2019-08-13  1:33       ` Joel Fernandes
2019-08-13 12:30       ` Frederic Weisbecker
2019-08-13 14:48         ` Paul E. McKenney
2019-08-14 17:55           ` Joel Fernandes
2019-08-14 22:05             ` Paul E. McKenney
2019-08-15 15:07               ` Joel Fernandes
2019-08-15 17:23                 ` Paul E. McKenney
2019-08-15 18:15                   ` Joel Fernandes
2019-08-15 18:39                     ` Paul E. McKenney
2019-08-15 19:42                       ` Joel Fernandes
2019-08-13 21:06       ` Paul E. McKenney

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