Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency and identical stores

On Thu, Feb 25, 2016 at 03:48:38PM +0100, Peter Zijlstra wrote: > On Thu, Feb 25, 2016 at 06:07:03AM -0800, Paul E. McKenney wrote: > > Still bad wording... > > > > It hasn't actually moved anything over the barrier(). It has instead > > moved both the barrier() and the WRITE_ONCE(b, p) to

Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency and identical stores

On Thu, Feb 25, 2016 at 03:48:38PM +0100, Peter Zijlstra wrote: > On Thu, Feb 25, 2016 at 06:07:03AM -0800, Paul E. McKenney wrote: > > Still bad wording... > > > > It hasn't actually moved anything over the barrier(). It has instead > > moved both the barrier() and the WRITE_ONCE(b, p) to

Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency and identical stores

On Thu, Feb 25, 2016 at 06:07:03AM -0800, Paul E. McKenney wrote: > Still bad wording... > > It hasn't actually moved anything over the barrier(). It has instead > moved both the barrier() and the WRITE_ONCE(b, p) to precede the "if > (q)". Mathieu mentioned this over IRC yesterday, and I queue

Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency and identical stores

On Thu, Feb 25, 2016 at 06:07:03AM -0800, Paul E. McKenney wrote: > Still bad wording... > > It hasn't actually moved anything over the barrier(). It has instead > moved both the barrier() and the WRITE_ONCE(b, p) to precede the "if > (q)". Mathieu mentioned this over IRC yesterday, and I queue

Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency and identical stores

On Thu, Feb 25, 2016 at 02:41:07PM +0800, Jianyu Zhan wrote: > On Thu, Feb 25, 2016 at 5:40 AM, Paul E. McKenney > wrote: > > So ordering between the read from "a" and the write to "b" is still > > preserved. The reason this works is that the smp_mb() does all the > >

Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency and identical stores

On Thu, Feb 25, 2016 at 02:41:07PM +0800, Jianyu Zhan wrote: > On Thu, Feb 25, 2016 at 5:40 AM, Paul E. McKenney > wrote: > > So ordering between the read from "a" and the write to "b" is still > > preserved. The reason this works is that the smp_mb() does all the > > ordering, so the fact that

Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency and identical stores

On Thu, Feb 25, 2016 at 09:21:43AM +0100, Peter Zijlstra wrote: > On Wed, Feb 24, 2016 at 01:40:13PM -0800, Paul E. McKenney wrote: > > > > + (*) If both legs of the "if" statement begin with identical stores to > > > > + the same variable, then those stores must be ordered, either by > > >

Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency and identical stores

On Thu, Feb 25, 2016 at 09:21:43AM +0100, Peter Zijlstra wrote: > On Wed, Feb 24, 2016 at 01:40:13PM -0800, Paul E. McKenney wrote: > > > > + (*) If both legs of the "if" statement begin with identical stores to > > > > + the same variable, then those stores must be ordered, either by > > >

Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency and identical stores

On Wed, Feb 24, 2016 at 01:40:13PM -0800, Paul E. McKenney wrote: > > > + (*) If both legs of the "if" statement begin with identical stores to > > > + the same variable, then those stores must be ordered, either by > > > + preceding both of them with smp_mb() or by using > > >

Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency and identical stores

On Wed, Feb 24, 2016 at 01:40:13PM -0800, Paul E. McKenney wrote: > > > + (*) If both legs of the "if" statement begin with identical stores to > > > + the same variable, then those stores must be ordered, either by > > > + preceding both of them with smp_mb() or by using > > >

Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency and identical stores

On Thu, Feb 25, 2016 at 5:40 AM, Paul E. McKenney wrote: > So ordering between the read from "a" and the write to "b" is still > preserved. The reason this works is that the smp_mb() does all the > ordering, so the fact that the control dependency has been eliminated

Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency and identical stores

On Thu, Feb 25, 2016 at 5:40 AM, Paul E. McKenney wrote: > So ordering between the read from "a" and the write to "b" is still > preserved. The reason this works is that the smp_mb() does all the > ordering, so the fact that the control dependency has been eliminated > is irrelevant. Thanks,

Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency and identical stores

On Wed, Feb 24, 2016 at 09:12:04PM +, Mathieu Desnoyers wrote: > - On Feb 24, 2016, at 12:00 AM, Paul E. McKenney > paul...@linux.vnet.ibm.com wrote: > > > The summary of the "CONTROL DEPENDENCIES" section incorrectly states that > > barrier() may be used to prevent compiler reordering

Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency and identical stores

On Wed, Feb 24, 2016 at 09:12:04PM +, Mathieu Desnoyers wrote: > - On Feb 24, 2016, at 12:00 AM, Paul E. McKenney > paul...@linux.vnet.ibm.com wrote: > > > The summary of the "CONTROL DEPENDENCIES" section incorrectly states that > > barrier() may be used to prevent compiler reordering

Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency and identical stores

- On Feb 24, 2016, at 12:00 AM, Paul E. McKenney paul...@linux.vnet.ibm.com wrote: > The summary of the "CONTROL DEPENDENCIES" section incorrectly states that > barrier() may be used to prevent compiler reordering when more than one > leg of the control-dependent "if" statement start with

Re: [PATCH tip/core/rcu 02/14] documentation: Fix control dependency and identical stores

- On Feb 24, 2016, at 12:00 AM, Paul E. McKenney paul...@linux.vnet.ibm.com wrote: > The summary of the "CONTROL DEPENDENCIES" section incorrectly states that > barrier() may be used to prevent compiler reordering when more than one > leg of the control-dependent "if" statement start with

[PATCH tip/core/rcu 02/14] documentation: Fix control dependency and identical stores

The summary of the "CONTROL DEPENDENCIES" section incorrectly states that barrier() may be used to prevent compiler reordering when more than one leg of the control-dependent "if" statement start with identical stores. This is incorrect at high optimization levels. This commit therefore updates

[PATCH tip/core/rcu 02/14] documentation: Fix control dependency and identical stores

The summary of the "CONTROL DEPENDENCIES" section incorrectly states that barrier() may be used to prevent compiler reordering when more than one leg of the control-dependent "if" statement start with identical stores. This is incorrect at high optimization levels. This commit therefore updates