perf, core: Rate limit perf_sched_events jump_label patching

jump_lable patching is very expensive operation that involves pausing all
cpus. The patching of perf_sched_events jump_label is easily controllable
from userspace by unprivileged user.

When te user runs a loop like this:

  "while true; do perf stat -e cycles true; done"

... the performance of my test application that just increments a counter
for one second drops by 4%.

This is on a 16 cpu box with my test application using only one of
them. An impact on a real server doing real work will be worse.

Performance of KVM PMU drops nearly 50% due to jump_lable for "perf
record" since KVM PMU implementation creates and destroys perf event
frequently.

This patch introduces a way to rate limit jump_label patching and uses
it to fix the above problem.

I believe that as jump_label use will spread the problem will become more
common and thus solving it in a generic code is appropriate. Also fixing
it in the perf code would result in moving jump_label accounting logic to
perf code with all the ifdefs in case of JUMP_LABEL=n kernel. With this
patch all details are nicely hidden inside jump_label code.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Acked-by: Jason Baron <jbaron@redhat.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20111127155909.GO2557@redhat.com
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 33 insertions, 2 deletions

diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index 66ff7109f69..51a175ab0a0 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -72,15 +72,46 @@ void jump_label_inc(struct jump_label_key *key)
 	jump_label_unlock();
 }
 
-void jump_label_dec(struct jump_label_key *key)
+static void __jump_label_dec(struct jump_label_key *key,
+		unsigned long rate_limit, struct delayed_work *work)
 {
 	if (!atomic_dec_and_mutex_lock(&key->enabled, &jump_label_mutex))
 		return;
 
-	jump_label_update(key, JUMP_LABEL_DISABLE);
+	if (rate_limit) {
+		atomic_inc(&key->enabled);
+		schedule_delayed_work(work, rate_limit);
+	} else
+		jump_label_update(key, JUMP_LABEL_DISABLE);
+
 	jump_label_unlock();
 }
 
+static void jump_label_update_timeout(struct work_struct *work)
+{
+	struct jump_label_key_deferred *key =
+		container_of(work, struct jump_label_key_deferred, work.work);
+	__jump_label_dec(&key->key, 0, NULL);
+}
+
+void jump_label_dec(struct jump_label_key *key)
+{
+	__jump_label_dec(key, 0, NULL);
+}
+
+void jump_label_dec_deferred(struct jump_label_key_deferred *key)
+{
+	__jump_label_dec(&key->key, key->timeout, &key->work);
+}
+
+
+void jump_label_rate_limit(struct jump_label_key_deferred *key,
+		unsigned long rl)
+{
+	key->timeout = rl;
+	INIT_DELAYED_WORK(&key->work, jump_label_update_timeout);
+}
+
 static int addr_conflict(struct jump_entry *entry, void *start, void *end)
 {
 	if (entry->code <= (unsigned long)end &&