On Tue, May 28, 2013 at 02:38:42PM -0400, Steven Rostedt wrote: > As rcu_dereference_raw() under RCU debug config options can add quite a > bit of checks, and that tracing uses rcu_dereference_raw(), these checks > happen with the function tracer. The function tracer also happens to trace > these debug checks too. This added overhead can livelock the system. > > Add a new interface to RCU for both rcu_dereference_raw_notrace() as well > as hlist_for_each_entry_rcu_notrace() as the hlist iterator uses the > rcu_dereference_raw() as well, and is used a bit with the function tracer. > > Signed-off-by: Steven Rostedt <rost...@goodmis.org>
Much nicer! Acked-by: Paul E. McKenney <paul...@linux.vnet.ibm.com> > Index: linux-trace.git/include/linux/rculist.h > =================================================================== > --- linux-trace.git.orig/include/linux/rculist.h > +++ linux-trace.git/include/linux/rculist.h > @@ -461,6 +461,26 @@ static inline void hlist_add_after_rcu(s > &(pos)->member)), typeof(*(pos)), member)) > > /** > + * hlist_for_each_entry_rcu_notrace - iterate over rcu list of given type > (for tracing) > + * @pos: the type * to use as a loop cursor. > + * @head: the head for your list. > + * @member: the name of the hlist_node within the struct. > + * > + * This list-traversal primitive may safely run concurrently with > + * the _rcu list-mutation primitives such as hlist_add_head_rcu() > + * as long as the traversal is guarded by rcu_read_lock(). > + * > + * This is the same as hlist_for_each_entry_rcu() except that it does > + * not do any RCU debugging or tracing. > + */ > +#define hlist_for_each_entry_rcu_notrace(pos, head, member) > \ > + for (pos = hlist_entry_safe > (rcu_dereference_raw_notrace(hlist_first_rcu(head)),\ > + typeof(*(pos)), member); \ > + pos; \ > + pos = > hlist_entry_safe(rcu_dereference_raw_notrace(hlist_next_rcu(\ > + &(pos)->member)), typeof(*(pos)), member)) > + > +/** > * hlist_for_each_entry_rcu_bh - iterate over rcu list of given type > * @pos: the type * to use as a loop cursor. > * @head: the head for your list. > Index: linux-trace.git/include/linux/rcupdate.h > =================================================================== > --- linux-trace.git.orig/include/linux/rcupdate.h > +++ linux-trace.git/include/linux/rcupdate.h > @@ -640,6 +640,15 @@ static inline void rcu_preempt_sleep_che > > #define rcu_dereference_raw(p) rcu_dereference_check(p, 1) /*@@@ needed? > @@@*/ > > +/* > + * The tracing infrastructure traces RCU (we want that), but unfortunately > + * some of the RCU checks causes tracing to lock up the system. > + * > + * The tracing version of rcu_dereference_raw() must not call > + * rcu_read_lock_held(). > + */ > +#define rcu_dereference_raw_notrace(p) __rcu_dereference_check((p), 1, __rcu) > + > /** > * rcu_access_index() - fetch RCU index with no dereferencing > * @p: The index to read > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
