On Tue, May 28, 2013 at 02:38:43PM -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. > > Have the function tracer use the new RCU _notrace equivalents that do > not do the debug checks for RCU. > > Signed-off-by: Steven Rostedt <[email protected]>
Looks good to me! Acked-by: Paul E. McKenney <[email protected]> > Index: linux-trace.git/kernel/trace/ftrace.c > =================================================================== > --- linux-trace.git.orig/kernel/trace/ftrace.c > +++ linux-trace.git/kernel/trace/ftrace.c > @@ -120,22 +120,22 @@ static void ftrace_ops_no_ops(unsigned l > > /* > * Traverse the ftrace_global_list, invoking all entries. The reason that we > - * can use rcu_dereference_raw() is that elements removed from this list > + * can use rcu_dereference_raw_notrace() is that elements removed from this > list > * are simply leaked, so there is no need to interact with a grace-period > - * mechanism. The rcu_dereference_raw() calls are needed to handle > + * mechanism. The rcu_dereference_raw_notrace() calls are needed to handle > * concurrent insertions into the ftrace_global_list. > * > * Silly Alpha and silly pointer-speculation compiler optimizations! > */ > #define do_for_each_ftrace_op(op, list) \ > - op = rcu_dereference_raw(list); \ > + op = rcu_dereference_raw_notrace(list); \ > do > > /* > * Optimized for just a single item in the list (as that is the normal case). > */ > #define while_for_each_ftrace_op(op) \ > - while (likely(op = rcu_dereference_raw((op)->next)) && \ > + while (likely(op = rcu_dereference_raw_notrace((op)->next)) && \ > unlikely((op) != &ftrace_list_end)) > > static inline void ftrace_ops_init(struct ftrace_ops *ops) > @@ -779,7 +779,7 @@ ftrace_find_profiled_func(struct ftrace_ > if (hlist_empty(hhd)) > return NULL; > > - hlist_for_each_entry_rcu(rec, hhd, node) { > + hlist_for_each_entry_rcu_notrace(rec, hhd, node) { > if (rec->ip == ip) > return rec; > } > @@ -1165,7 +1165,7 @@ ftrace_lookup_ip(struct ftrace_hash *has > > hhd = &hash->buckets[key]; > > - hlist_for_each_entry_rcu(entry, hhd, hlist) { > + hlist_for_each_entry_rcu_notrace(entry, hhd, hlist) { > if (entry->ip == ip) > return entry; > } > @@ -1422,8 +1422,8 @@ ftrace_ops_test(struct ftrace_ops *ops, > struct ftrace_hash *notrace_hash; > int ret; > > - filter_hash = rcu_dereference_raw(ops->filter_hash); > - notrace_hash = rcu_dereference_raw(ops->notrace_hash); > + filter_hash = rcu_dereference_raw_notrace(ops->filter_hash); > + notrace_hash = rcu_dereference_raw_notrace(ops->notrace_hash); > > if ((ftrace_hash_empty(filter_hash) || > ftrace_lookup_ip(filter_hash, ip)) && > @@ -2920,7 +2920,7 @@ static void function_trace_probe_call(un > * on the hash. rcu_read_lock is too dangerous here. > */ > preempt_disable_notrace(); > - hlist_for_each_entry_rcu(entry, hhd, node) { > + hlist_for_each_entry_rcu_notrace(entry, hhd, node) { > if (entry->ip == ip) > entry->ops->func(ip, parent_ip, &entry->data); > } > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
