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Commit b2029520 authored by Gleb Natapov's avatar Gleb Natapov Committed by Ingo Molnar
Browse files

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: default avatarGleb Natapov <gleb@redhat.com>
Acked-by: default avatarJason Baron <jbaron@redhat.com>
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20111127155909.GO2557@redhat.com


Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent b79387ef

include/linux/jump_label.h

+24 −0
Original line number Diff line number Diff line
@@ -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 */

include/linux/perf_event.h

+3 −3
Original line number Diff line number Diff line
@@ -1064,12 +1064,12 @@ 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);

}
@@ -1078,7 +1078,7 @@ 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);

}

kernel/events/core.c

+8 −5
Original line number Diff line number Diff line
@@ -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;
@@ -2748,7 +2748,7 @@ 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)
@@ -2759,7 +2759,7 @@ 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);

		}

	}
@@ -5784,7 +5784,7 @@ 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)
@@ -6022,7 +6022,7 @@ 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);

	}



	/*
@@ -6868,6 +6868,9 @@ 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)

kernel/jump_label.c

+33 −2
Original line number Diff line number Diff line
@@ -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;



	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 &&