From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Olof Johansson <olof@lixom.net>
Cc: linux-kernel@vger.kernel.org, mingo@elte.hu,
laijs@cn.fujitsu.com, dipankar@in.ibm.com,
akpm@linux-foundation.org, mathieu.desnoyers@polymtl.ca,
josh@joshtriplett.org, niv@us.ibm.com, tglx@linutronix.de,
peterz@infradead.org, rostedt@goodmis.org,
Valdis.Kletnieks@vt.edu, dhowells@redhat.com,
eric.dumazet@gmail.com, darren@dvhart.com, patches@linaro.org,
anton@samba.org, benh@kernel.crashing.org, paulus@samba.org,
linuxppc-dev@ozlabs.org
Subject: Re: [PATCH tip/core/rcu 48/55] powerpc: strengthen value-returning-atomics memory barriers
Date: Fri, 9 Sep 2011 10:34:55 -0700 [thread overview]
Message-ID: <20110909173455.GH2435@linux.vnet.ibm.com> (raw)
In-Reply-To: <CAOesGMi--W6TCUMZzF07-Zep9Ta3tBJWZcG+5imEK_Hza0y9Jg@mail.gmail.com>
On Fri, Sep 09, 2011 at 10:23:33AM -0700, Olof Johansson wrote:
> [+linuxppc-dev]
>
> On Tue, Sep 6, 2011 at 11:00 AM, Paul E. McKenney
> <paulmck@linux.vnet.ibm.com> wrote:
> > The trailing isync/lwsync in PowerPC value-returning atomics needs
> > to be a sync in order to provide the required ordering properties.
> > The leading lwsync/eieio can remain, as the remainder of the required
> > ordering guarantees are provided by the atomic instructions: Any
> > reordering will cause the stwcx to fail, which will result in a retry.
>
> Admittedly, my powerpc barrier memory is starting to fade, but isn't
> isync sufficient here? It will make sure all instructions before it
> have retired, and will restart any speculative/issued instructions
> beyond it.
>
> lwsync not being sufficient makes sense since a load can overtake it.
As I understand it, although isync waits for the prior stwcx to execute,
it does not guarantee that the corresponding store is visible to all
processors before any following loads.
> > diff --git a/arch/powerpc/include/asm/synch.h b/arch/powerpc/include/asm/synch.h
> > index d7cab44..4d97fbe 100644
> > --- a/arch/powerpc/include/asm/synch.h
> > +++ b/arch/powerpc/include/asm/synch.h
> > @@ -37,11 +37,7 @@ static inline void isync(void)
> > #endif
> >
> > #ifdef CONFIG_SMP
> > -#define __PPC_ACQUIRE_BARRIER \
> > - START_LWSYNC_SECTION(97); \
> > - isync; \
> > - MAKE_LWSYNC_SECTION_ENTRY(97, __lwsync_fixup);
> > -#define PPC_ACQUIRE_BARRIER "\n" stringify_in_c(__PPC_ACQUIRE_BARRIER)
> > +#define PPC_ACQUIRE_BARRIER "\n" stringify_in_c(sync;)
>
> This can just be done as "\n\tsync\n" instead of the stringify stuff.
That does sound a bit more straightforward, now that you mention it. ;-)
Thanx, Paul
next prev parent reply other threads:[~2011-09-09 17:35 UTC|newest]
Thread overview: 98+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-06 18:00 [PATCH tip/core/rcu 0/55] Preview of RCU changes for 3.2 Paul E. McKenney
2011-09-06 17:59 ` [PATCH tip/core/rcu 01/55] rcu: Use kthread_create_on_node() Paul E. McKenney
2011-09-06 17:59 ` [PATCH tip/core/rcu 02/55] rcu: Avoid unnecessary self-wakeup of per-CPU kthreads Paul E. McKenney
2011-09-06 17:59 ` [PATCH tip/core/rcu 03/55] rcu: Update documentation to flag RCU_BOOST trace information Paul E. McKenney
2011-09-06 17:59 ` [PATCH tip/core/rcu 04/55] rcu: Restore checks for blocking in RCU read-side critical sections Paul E. McKenney
2011-09-06 17:59 ` [PATCH tip/core/rcu 05/55] rcu: Move rcu_head definition to types.h Paul E. McKenney
2011-09-07 18:31 ` Paul Gortmaker
2011-09-07 22:11 ` Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 06/55] rcu: Update rcutorture documentation Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 07/55] rcu: Fix mismatched variable in rcutree_trace.c Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 08/55] rcu: Abstract common code for RCU grace-period-wait primitives Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 09/55] rcu: Catch rcutorture up to new RCU API additions Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 10/55] rcu: Fix RCU's NMI documentation Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 11/55] rcu: Drive configuration directly from SMP and PREEMPT Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 12/55] rcu: Fix pathnames in documentation Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 13/55] rcu: Don't destroy rcu_torture_boost() callback until it is done Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 14/55] rcu: Add event-tracing for RCU callback invocation Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 15/55] rcu: Event-trace markers for computing RCU CPU utilization Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 16/55] rcu: Put names into TINY_RCU structures under RCU_TRACE Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 17/55] rcu: Add RCU type to callback-invocation tracing Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 18/55] rcu: Update comments to reflect softirqs vs. kthreads Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 19/55] rcu: Move RCU_BOOST declarations to allow compiler checking Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 20/55] rcu: Add event-trace markers to TREE_RCU kthreads Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 21/55] rcu: Make TINY_RCU also use softirq for RCU_BOOST=n Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 22/55] rcu: Add grace-period, quiescent-state, and call_rcu trace events Paul E. McKenney
2011-10-17 1:33 ` Josh Triplett
2011-10-24 12:02 ` Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 23/55] rcu: Simplify quiescent-state accounting Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 24/55] rcu: Not necessary to pass rcu_read_lock_held() to rcu_dereference_protected() Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 25/55] rcu: Update documentation for additional RCU lockdep functions Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 26/55] rcu: Remove unused and redundant interfaces Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 27/55] rcu: Allow rcutorture's stat_interval parameter to be changed at runtime Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 28/55] rcu: Document interpretation of RCU-lockdep splats Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 29/55] nohz: Remove nohz_cpu_mask Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 30/55] rcu: Eliminate in_irq() checks in rcu_enter_nohz() Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 31/55] rcu: Make rcu_implicit_dynticks_qs() locals be correct size Paul E. McKenney
2011-10-17 1:43 ` Josh Triplett
2011-10-24 12:00 ` Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 32/55] rcu: Make rcu_assign_pointer() unconditionally insert a memory barrier Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 33/55] rcu: Improve rcu_assign_pointer() and RCU_INIT_POINTER() documentation Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 34/55] rcu: Move __rcu_read_unlock()'s barrier() within if-statement Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 35/55] rcu: Dump local stack if cannot dump all CPUs' stacks Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 36/55] rcu: Prevent early boot set_need_resched() from __rcu_pending() Paul E. McKenney
2011-10-17 1:49 ` Josh Triplett
2011-10-24 12:07 ` Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 37/55] rcu: Simplify unboosting checks Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 38/55] rcu: Prohibit grace periods during early boot Paul E. McKenney
2011-10-17 1:51 ` Josh Triplett
2011-09-06 18:00 ` [PATCH tip/core/rcu 39/55] rcu: Suppress NMI backtraces when stall ends before dump Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 40/55] rcu: Avoid having just-onlined CPU resched itself when RCU is idle Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 41/55] rcu: Permit rt_mutex_unlock() with irqs disabled Paul E. McKenney
2011-09-18 4:09 ` Yong Zhang
2011-09-19 4:14 ` Paul E. McKenney
2011-09-19 5:49 ` Yong Zhang
2011-09-20 14:57 ` Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 42/55] rcu: Make rcu_torture_fqs() exit loops at end of test Paul E. McKenney
2011-10-17 1:53 ` Josh Triplett
2011-10-24 12:10 ` Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 43/55] rcu: Make rcu_torture_boost() " Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 44/55] rcu: wire up RCU_BOOST_PRIO for rcutree Paul E. McKenney
2011-09-13 12:02 ` Mike Galbraith
2011-09-13 15:34 ` Paul E. McKenney
2011-09-13 16:04 ` Mike Galbraith
2011-09-13 20:50 ` Paul E. McKenney
2011-10-17 1:55 ` Josh Triplett
2011-09-06 18:00 ` [PATCH tip/core/rcu 45/55] rcu: check for entering dyntick-idle mode while in read-side critical section Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 46/55] rcu: Remove rcu_needs_cpu_flush() to avoid false quiescent states Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 47/55] rcu: Move propagation of ->completed from rcu_start_gp() to rcu_report_qs_rsp() Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 48/55] powerpc: strengthen value-returning-atomics memory barriers Paul E. McKenney
2011-09-09 17:23 ` Olof Johansson
2011-09-09 17:34 ` Paul E. McKenney [this message]
2011-09-09 18:43 ` Olof Johansson
2011-09-06 18:00 ` [PATCH tip/core/rcu 49/55] rcu: Detect illegal rcu dereference in extended quiescent state Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 50/55] rcu: Inform the user about dynticks-idle mode on PROVE_RCU warning Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 51/55] rcu: Warn when rcu_read_lock() is used in extended quiescent state Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 52/55] rcu: Remove one layer of abstraction from PROVE_RCU checking Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 53/55] rcu: Warn when srcu_read_lock() is used in an extended quiescent state Paul E. McKenney
2011-10-04 21:03 ` Frederic Weisbecker
2011-10-04 23:40 ` Paul E. McKenney
2011-10-04 23:42 ` Frederic Weisbecker
2011-09-06 18:00 ` [PATCH tip/core/rcu 54/55] rcu: Make srcu_read_lock_held() call common lockdep-enabled function Paul E. McKenney
2011-10-17 2:03 ` Josh Triplett
2011-10-24 12:34 ` Paul E. McKenney
2011-09-06 18:00 ` [PATCH tip/core/rcu 55/55] powerpc: Work around tracing from dyntick-idle mode Paul E. McKenney
2011-09-07 10:00 ` Benjamin Herrenschmidt
2011-09-07 13:44 ` Paul E. McKenney
2011-09-13 19:13 ` Frederic Weisbecker
2011-09-13 19:50 ` Paul E. McKenney
2011-09-13 20:49 ` Benjamin Herrenschmidt
2011-09-15 14:53 ` Frederic Weisbecker
2011-09-16 12:24 ` Frederic Weisbecker
2011-09-07 14:39 ` [PATCH tip/core/rcu 0/55] Preview of RCU changes for 3.2 Lin Ming
2011-09-08 17:41 ` Paul E. McKenney
2011-09-08 19:23 ` Thomas Gleixner
2011-09-08 20:48 ` Paul E. McKenney
2011-09-12 16:24 ` Paul E. McKenney
2011-10-17 2:06 ` Josh Triplett
2011-10-24 12:35 ` Paul E. McKenney
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