Messages in this thread | | | Date | Mon, 16 Jan 2017 10:57:04 -0800 | From | Josh Triplett <> | Subject | Re: [PATCH tip/core/rcu 1/6] rcu: Abstract the dynticks momentary-idle operation |
| |
On Mon, Jan 16, 2017 at 03:22:39AM -0800, Paul E. McKenney wrote: > On Sun, Jan 15, 2017 at 11:39:51PM -0800, Josh Triplett wrote: > > On Sat, Jan 14, 2017 at 12:54:40AM -0800, Paul E. McKenney wrote: > > > This commit is the first step towards full abstraction of all accesses to > > > the ->dynticks counter, implementing the previously open-coded atomic add > > > of two in a new rcu_dynticks_momentary_idle() function. This abstraction > > > will ease changes to the ->dynticks counter operation. > > > > > > Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com> > > > > This change has an additional effect not documented in the commit > > message: it eliminates the smp_mb__before_atomic and > > smp_mb__after_atomic calls. Can you please document that in the commit > > message, and explain why that doesn't cause a problem? > > The trick is that the old code used the non-value-returning atomic_add(), > which does not imply ordering, hence the smp_mb__before_atomic() and > smp_mb__after_atomic() calls. The new code uses atomic_add_return(), > which does return a value, and therefore implies full ordering in and > of itself. > > How would you like me to proceed?
With the above explanation added to the commit message:
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
| |