b202952075
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>
131 lines
3 KiB
C
131 lines
3 KiB
C
#ifndef _LINUX_JUMP_LABEL_H
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#define _LINUX_JUMP_LABEL_H
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#include <linux/types.h>
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#include <linux/compiler.h>
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#include <linux/workqueue.h>
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#if defined(CC_HAVE_ASM_GOTO) && defined(CONFIG_JUMP_LABEL)
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struct jump_label_key {
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atomic_t enabled;
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struct jump_entry *entries;
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#ifdef CONFIG_MODULES
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struct jump_label_mod *next;
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#endif
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};
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struct jump_label_key_deferred {
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struct jump_label_key key;
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unsigned long timeout;
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struct delayed_work work;
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};
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# include <asm/jump_label.h>
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# define HAVE_JUMP_LABEL
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#endif /* CC_HAVE_ASM_GOTO && CONFIG_JUMP_LABEL */
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enum jump_label_type {
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JUMP_LABEL_DISABLE = 0,
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JUMP_LABEL_ENABLE,
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};
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struct module;
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#ifdef HAVE_JUMP_LABEL
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#ifdef CONFIG_MODULES
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#define JUMP_LABEL_INIT {ATOMIC_INIT(0), NULL, NULL}
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#else
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#define JUMP_LABEL_INIT {ATOMIC_INIT(0), NULL}
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#endif
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static __always_inline bool static_branch(struct jump_label_key *key)
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{
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return arch_static_branch(key);
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}
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extern struct jump_entry __start___jump_table[];
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extern struct jump_entry __stop___jump_table[];
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extern void jump_label_init(void);
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extern void jump_label_lock(void);
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extern void jump_label_unlock(void);
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extern void arch_jump_label_transform(struct jump_entry *entry,
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enum jump_label_type type);
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extern void arch_jump_label_transform_static(struct jump_entry *entry,
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enum jump_label_type type);
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extern int jump_label_text_reserved(void *start, void *end);
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extern void jump_label_inc(struct jump_label_key *key);
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extern void jump_label_dec(struct jump_label_key *key);
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extern void jump_label_dec_deferred(struct jump_label_key_deferred *key);
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extern bool jump_label_enabled(struct jump_label_key *key);
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extern void jump_label_apply_nops(struct module *mod);
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extern void jump_label_rate_limit(struct jump_label_key_deferred *key,
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unsigned long rl);
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#else /* !HAVE_JUMP_LABEL */
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#include <linux/atomic.h>
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#define JUMP_LABEL_INIT {ATOMIC_INIT(0)}
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struct jump_label_key {
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atomic_t enabled;
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};
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static __always_inline void jump_label_init(void)
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{
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}
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struct jump_label_key_deferred {
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struct jump_label_key key;
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};
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static __always_inline bool static_branch(struct jump_label_key *key)
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{
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if (unlikely(atomic_read(&key->enabled)))
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return true;
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return false;
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}
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static inline void jump_label_inc(struct jump_label_key *key)
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{
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atomic_inc(&key->enabled);
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}
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static inline void jump_label_dec(struct jump_label_key *key)
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{
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atomic_dec(&key->enabled);
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}
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static inline void jump_label_dec_deferred(struct jump_label_key_deferred *key)
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{
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jump_label_dec(&key->key);
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}
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static inline int jump_label_text_reserved(void *start, void *end)
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{
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return 0;
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}
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static inline void jump_label_lock(void) {}
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static inline void jump_label_unlock(void) {}
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static inline bool jump_label_enabled(struct jump_label_key *key)
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{
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return !!atomic_read(&key->enabled);
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}
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static inline int jump_label_apply_nops(struct module *mod)
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{
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return 0;
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}
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static inline void jump_label_rate_limit(struct jump_label_key_deferred *key,
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unsigned long rl)
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{
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}
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#endif /* HAVE_JUMP_LABEL */
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#endif /* _LINUX_JUMP_LABEL_H */
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