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>
diff --git a/kernel/jump_label.c b/kernel/jump_label.c
index 66ff710..51a175a 100644
--- a/kernel/jump_label.c
+++ b/kernel/jump_label.c
@@ -72,15 +72,46 @@
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 &&
