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From: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
To: Will Deacon <will.deacon@arm.com>
Cc: Hannes Frederic Sowa <hannes@stressinduktion.org>,
	Peter Zijlstra <peterz@infradead.org>,
	Vineet Gupta <Vineet.Gupta1@synopsys.com>,
	Waiman Long <waiman.long@hpe.com>,
	linux-kernel@vger.kernel.org, torvalds@linux-foundation.org,
	manfred@colorfullife.com, dave@stgolabs.net,
	boqun.feng@gmail.com, tj@kernel.org, pablo@netfilter.org,
	kaber@trash.net, davem@davemloft.net, oleg@redhat.com,
	netfilter-devel@vger.kernel.org, sasha.levin@oracle.com,
	hofrat@osadl.org
Subject: Re: [RFC][PATCH 1/3] locking: Introduce smp_acquire__after_ctrl_dep
Date: Tue, 7 Jun 2016 11:44:41 -0700	[thread overview]
Message-ID: <20160607184441.GH3723@linux.vnet.ibm.com> (raw)
In-Reply-To: <20160607180106.GD20477@arm.com>

On Tue, Jun 07, 2016 at 07:01:07PM +0100, Will Deacon wrote:
> On Tue, Jun 07, 2016 at 08:23:15AM -0700, Paul E. McKenney wrote:
> > On Tue, Jun 07, 2016 at 04:59:02PM +0200, Hannes Frederic Sowa wrote:
> > > Sorry, to follow-up again on this. Will Deacon's comments were about
> > > conditional-move instructions, which this compiler-option would prevent,
> > > as far as I can see it.
> > 
> > According to this email thread, I believe that this works the other
> > way around:
> > 
> > http://thread.gmane.org/gmane.linux.kernel/1721993
> > 
> > That parameter prevents the compiler from converting a conditional
> > store into an unconditional store, which would be really problematic.
> > Give the current kernel build, I believe that the compiler really is
> > within its rights to use conditional-move instructions as shown above.
> > But I again must defer to Will Deacon on the details.
> 
> A multi_v7_defconfig build of mainline certainly spits out conditional
> store instructions, but I have no idea whether these correspond to
> WRITE_ONCE or not:
> 
> $ objdump -d vmlinux | grep 'str\(eq\|ne\)' | wc -l
> 7326
> 
> At the end of the day, the ARM architecture says you can't rely on this
> being ordered and I can see it happening in practice in the face of
> conditional stores.

Thank you for the info, Will!

							Thanx, Paul

  reply	other threads:[~2016-06-07 18:44 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-05-24 14:27 [RFC][PATCH 0/3] spin_unlock_wait and assorted borkage Peter Zijlstra
2016-05-24 14:27 ` [RFC][PATCH 1/3] locking: Introduce smp_acquire__after_ctrl_dep Peter Zijlstra
     [not found]   ` <57451581.6000700@hpe.com>
2016-05-25  4:53     ` Paul E. McKenney
2016-05-25  5:39       ` Boqun Feng
2016-05-25 14:29         ` Paul E. McKenney
2016-05-25 15:20       ` Waiman Long
2016-05-25 15:57         ` Paul E. McKenney
2016-05-25 16:28           ` Peter Zijlstra
2016-05-25 16:54             ` Linus Torvalds
2016-05-25 18:59               ` Paul E. McKenney
2016-06-03  9:18           ` Vineet Gupta
2016-06-03  9:38             ` Peter Zijlstra
2016-06-03 12:08               ` Paul E. McKenney
2016-06-03 12:23                 ` Peter Zijlstra
2016-06-03 12:27                   ` Peter Zijlstra
2016-06-03 13:33                     ` Paul E. McKenney
2016-06-03 13:32                   ` Paul E. McKenney
2016-06-03 13:45                     ` Will Deacon
2016-06-04 15:29                       ` Paul E. McKenney
2016-06-06 17:28                         ` Paul E. McKenney
2016-06-07  7:15                           ` Peter Zijlstra
2016-06-07 12:41                             ` Hannes Frederic Sowa
2016-06-07 13:06                               ` Paul E. McKenney
2016-06-07 14:59                                 ` Hannes Frederic Sowa
2016-06-07 15:23                                   ` Paul E. McKenney
2016-06-07 17:48                                     ` Peter Zijlstra
2016-06-07 18:44                                       ` Paul E. McKenney
2016-06-07 18:01                                     ` Will Deacon
2016-06-07 18:44                                       ` Paul E. McKenney [this message]
2016-06-07 18:54                                       ` Paul E. McKenney
2016-06-07 18:37                                     ` Hannes Frederic Sowa
2016-05-24 14:27 ` [RFC][PATCH 2/3] locking: Annotate spin_unlock_wait() users Peter Zijlstra
2016-05-24 16:17   ` Linus Torvalds
2016-05-24 16:22     ` Tejun Heo
2016-05-24 16:58       ` Peter Zijlstra
2016-05-25 19:28         ` Tejun Heo
2016-05-24 16:57     ` Peter Zijlstra
2016-05-24 14:27 ` [RFC][PATCH 3/3] locking,netfilter: Fix nf_conntrack_lock() Peter Zijlstra
2016-05-24 14:42   ` Peter Zijlstra
     [not found]   ` <3e1671fc-be0f-bc95-4fbb-6bfc56e6c15b@colorfullife.com>
2016-05-26 13:54     ` Peter Zijlstra

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