On Sat, Dec 01, 2007 at 12:07:52PM +1100, Herbert Xu wrote: > On Fri, Nov 30, 2007 at 04:37:21PM -0800, Paul E. McKenney wrote: > > > > The rcu_assign_pointer() primitive currently unconditionally executes > > a memory barrier, even when a NULL pointer is being assigned. This > > has lead some to avoid using rcu_assign_pointer() for NULL pointers, > > which loses the self-documenting advantages of rcu_assign_pointer() > > This patch uses __builtin_const_p() to omit needless memory barriers > > for NULL-pointer assignments at compile time with no runtime penalty, > > as discussed in the following thread: > > > > http://www.mail-archive.com/netdev@xxxxxxxxxxxxxxx/msg54852.html > > > > Tested on x86_64 and ppc64, also compiled the four cases (NULL/non-NULL > > and const/non-const) with gcc version 4.1.2, and hand-checked the > > assembly output. > > > > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> > > Acked-by: Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx> > > Thanks a lot for following through with this Paul! No problem -- after all, it is not every day that one gets the opportunity to make a simple change that speeds things up and makes kernel hackers lives a bit simpler. ;-) Thanx, Paul _______________________________________________ Bridge mailing list Bridge@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linux-foundation.org/mailman/listinfo/bridge
