On Fri, 2013-09-27 at 09:12 -0700, Jason Low wrote: > On Fri, 2013-09-27 at 08:02 +0200, Ingo Molnar wrote: > > Would be nice to have this as a separate, add-on patch. Every single > > instruction removal that has no downside is an upside! > > Okay, so here is a patch. Tim, would you like to add this to v7? Okay. Will do. Tim > > ... > Subject: MCS lock: Remove and reorder unnecessary assignments in mcs_spin_lock() > > In mcs_spin_lock(), if (likely(prev == NULL)) is true, then the lock is free > and we won't spin on the local node. In that case, we don't have to assign > node->locked because it won't be used. We can also move the node->locked = 0 > assignment so that it occurs after the if (likely(prev == NULL)) check. > > This might also help make it clearer as to how the node->locked variable > is used in MCS locks. > > Signed-off-by: Jason Low <jason.low2@xxxxxx> > --- > include/linux/mcslock.h | 3 +-- > 1 files changed, 1 insertions(+), 2 deletions(-) > > diff --git a/include/linux/mcslock.h b/include/linux/mcslock.h > index 20fd3f0..1167d57 100644 > --- a/include/linux/mcslock.h > +++ b/include/linux/mcslock.h > @@ -21,15 +21,14 @@ void mcs_spin_lock(struct mcs_spin_node **lock, struct mcs_spin_node *node) > struct mcs_spin_node *prev; > > /* Init node */ > - node->locked = 0; > node->next = NULL; > > prev = xchg(lock, node); > if (likely(prev == NULL)) { > /* Lock acquired */ > - node->locked = 1; > return; > } > + node->locked = 0; > ACCESS_ONCE(prev->next) = node; > smp_wmb(); > /* Wait until the lock holder passes the lock down */ -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx"> email@xxxxxxxxx </a>