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Message-ID: <20111127155909.GO2557@redhat.com>
Date: Sun, 27 Nov 2011 17:59:09 +0200
From: Gleb Natapov <gleb@...hat.com>
To: linux-kernel@...r.kernel.org
Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>, mingo@...e.hu,
Jason Baron <jbaron@...hat.com>, rostedt <rostedt@...dmis.org>,
Thomas Gleixner <tglx@...utronix.de>
Subject: [PATCH] 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 user runs 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 much 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 introduce the way to rate limit jump_label patching and uses
it to fix 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 a perf code will 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@...hat.com>
diff --git a/include/linux/jump_label.h b/include/linux/jump_label.h
index 388b0d4..22509cd 100644
--- a/include/linux/jump_label.h
+++ b/include/linux/jump_label.h
@@ -3,6 +3,7 @@
#include <linux/types.h>
#include <linux/compiler.h>
+#include <linux/workqueue.h>
#if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)
@@ -14,6 +15,12 @@ struct jump_label_key {
#endif
};
+struct jump_label_key_deferred {
+ struct jump_label_key key;
+ unsigned long timeout;
+ struct delayed_work work;
+};
+
# include <asm/jump_label.h>
# define HAVE_JUMP_LABEL
#endif /* CC_HAVE_ASM_GOTO && CONFIG_JUMP_LABEL */
@@ -51,8 +58,11 @@ extern void arch_jump_label_transform_static(struct jump_entry *entry,
extern int jump_label_text_reserved(void *start, void *end);
extern void jump_label_inc(struct jump_label_key *key);
extern void jump_label_dec(struct jump_label_key *key);
+extern void jump_label_dec_deferred(struct jump_label_key_deferred *key);
extern bool jump_label_enabled(struct jump_label_key *key);
extern void jump_label_apply_nops(struct module *mod);
+extern void jump_label_rate_limit(struct jump_label_key_deferred *key,
+ unsigned long rl);
#else /* !HAVE_JUMP_LABEL */
@@ -68,6 +78,10 @@ static __always_inline void jump_label_init(void)
{
}
+struct jump_label_key_deferred {
+ struct jump_label_key key;
+};
+
static __always_inline bool static_branch(struct jump_label_key *key)
{
if (unlikely(atomic_read(&key->enabled)))
@@ -85,6 +99,11 @@ static inline void jump_label_dec(struct jump_label_key *key)
atomic_dec(&key->enabled);
}
+static inline void jump_label_dec_deferred(struct jump_label_key_deferred *key)
+{
+ jump_label_dec(&key->key);
+}
+
static inline int jump_label_text_reserved(void *start, void *end)
{
return 0;
@@ -102,6 +121,11 @@ static inline int jump_label_apply_nops(struct module *mod)
{
return 0;
}
+
+static inline void jump_label_rate_limit(struct jump_label_key_deferred *key,
+ unsigned long rl)
+{
+}
#endif /* HAVE_JUMP_LABEL */
#endif /* _LINUX_JUMP_LABEL_H */
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 1e9ebe5..2272238 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1062,12 +1063,12 @@ perf_sw_event(u32 event_id, u64 nr, struct pt_regs *regs, u64 addr)
}
}
-extern struct jump_label_key perf_sched_events;
+extern struct jump_label_key_deferred perf_sched_events;
static inline void perf_event_task_sched_in(struct task_struct *prev,
struct task_struct *task)
{
- if (static_branch(&perf_sched_events))
+ if (static_branch(&perf_sched_events.key))
__perf_event_task_sched_in(prev, task);
}
@@ -1076,7 +1077,7 @@ static inline void perf_event_task_sched_out(struct task_struct *prev,
{
perf_sw_event(PERF_COUNT_SW_CONTEXT_SWITCHES, 1, NULL, 0);
- if (static_branch(&perf_sched_events))
+ if (static_branch(&perf_sched_events.key))
__perf_event_task_sched_out(prev, next);
}
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 2e41c8e..7de5e68 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -128,7 +128,7 @@ enum event_type_t {
* perf_sched_events : >0 events exist
* perf_cgroup_events: >0 per-cpu cgroup events exist on this cpu
*/
-struct jump_label_key perf_sched_events __read_mostly;
+struct jump_label_key_deferred perf_sched_events __read_mostly;
static DEFINE_PER_CPU(atomic_t, perf_cgroup_events);
static atomic_t nr_mmap_events __read_mostly;
@@ -2736,7 +2736,7 @@ static void free_event(struct perf_event *event)
if (!event->parent) {
if (event->attach_state & PERF_ATTACH_TASK)
- jump_label_dec(&perf_sched_events);
+ jump_label_dec_deferred(&perf_sched_events);
if (event->attr.mmap || event->attr.mmap_data)
atomic_dec(&nr_mmap_events);
if (event->attr.comm)
@@ -2747,7 +2747,7 @@ static void free_event(struct perf_event *event)
put_callchain_buffers();
if (is_cgroup_event(event)) {
atomic_dec(&per_cpu(perf_cgroup_events, event->cpu));
- jump_label_dec(&perf_sched_events);
+ jump_label_dec_deferred(&perf_sched_events);
}
}
@@ -5695,7 +5695,7 @@ done:
if (!event->parent) {
if (event->attach_state & PERF_ATTACH_TASK)
- jump_label_inc(&perf_sched_events);
+ jump_label_inc(&perf_sched_events.key);
if (event->attr.mmap || event->attr.mmap_data)
atomic_inc(&nr_mmap_events);
if (event->attr.comm)
@@ -5931,7 +5931,7 @@ SYSCALL_DEFINE5(perf_event_open,
* - that may need work on context switch
*/
atomic_inc(&per_cpu(perf_cgroup_events, event->cpu));
- jump_label_inc(&perf_sched_events);
+ jump_label_inc(&perf_sched_events.key);
}
/*
@@ -6777,6 +6777,9 @@ void __init perf_event_init(void)
ret = init_hw_breakpoint();
WARN(ret, "hw_breakpoint initialization failed with: %d", ret);
+
+ /* do not patch jump label more than once per second */
+ jump_label_rate_limit(&perf_sched_events, HZ);
}
static int __init perf_event_sysfs_init(void)
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 @@ 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 &&
--
Gleb.
--
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