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perf, core: Rate limit perf_sched_events jump_label patching
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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 <[email protected]>
Acked-by: Jason Baron <[email protected]>
Signed-off-by: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ingo Molnar <[email protected]>
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Gleb Natapov authored and Ingo Molnar committed Dec 6, 2011
1 parent b79387e commit b202952
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Showing 4 changed files with 68 additions and 10 deletions.
24 changes: 24 additions & 0 deletions include/linux/jump_label.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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)

Expand All @@ -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 */
Expand Down Expand Up @@ -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 */

Expand All @@ -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)))
Expand All @@ -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;
Expand All @@ -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 */
6 changes: 3 additions & 3 deletions include/linux/perf_event.h
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Original file line number Diff line number Diff line change
Expand Up @@ -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);
}

Expand All @@ -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);
}

Expand Down
13 changes: 8 additions & 5 deletions kernel/events/core.c
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Original file line number Diff line number Diff line change
Expand Up @@ -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;
Expand Down Expand Up @@ -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)
Expand All @@ -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);
}
}

Expand Down Expand Up @@ -5784,7 +5784,7 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,

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)
Expand Down Expand Up @@ -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);
}

/*
Expand Down Expand Up @@ -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)
Expand Down
35 changes: 33 additions & 2 deletions kernel/jump_label.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -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 &&
Expand Down

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