static keys: Introduce 'struct static_key', static_key_true()/false() and static_key_slow_[inc|dec]()
So here's a boot tested patch on top of Jason's series that does all the cleanups I talked about and turns jump labels into a more intuitive to use facility. It should also address the various misconceptions and confusions that surround jump labels. Typical usage scenarios: #include <linux/static_key.h> struct static_key key = STATIC_KEY_INIT_TRUE; if (static_key_false(&key)) do unlikely code else do likely code Or: if (static_key_true(&key)) do likely code else do unlikely code The static key is modified via: static_key_slow_inc(&key); ... static_key_slow_dec(&key); The 'slow' prefix makes it abundantly clear that this is an expensive operation. I've updated all in-kernel code to use this everywhere. Note that I (intentionally) have not pushed through the rename blindly through to the lowest levels: the actual jump-label patching arch facility should be named like that, so we want to decouple jump labels from the static-key facility a bit. On non-jump-label enabled architectures static keys default to likely()/unlikely() branches. Signed-off-by: Ingo Molnar <mingo@elte.hu> Acked-by: Jason Baron <jbaron@redhat.com> Acked-by: Steven Rostedt <rostedt@goodmis.org> Cc: a.p.zijlstra@chello.nl Cc: mathieu.desnoyers@efficios.com Cc: davem@davemloft.net Cc: ddaney.cavm@gmail.com Cc: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/20120222085809.GA26397@elte.hu Signed-off-by: Ingo Molnar <mingo@elte.hu>
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@@ -128,7 +128,7 @@ enum event_type_t {
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* perf_sched_events : >0 events exist
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* perf_cgroup_events: >0 per-cpu cgroup events exist on this cpu
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*/
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struct jump_label_key_deferred perf_sched_events __read_mostly;
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struct static_key_deferred perf_sched_events __read_mostly;
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static DEFINE_PER_CPU(atomic_t, perf_cgroup_events);
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static atomic_t nr_mmap_events __read_mostly;
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@@ -2769,7 +2769,7 @@ static void free_event(struct perf_event *event)
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if (!event->parent) {
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if (event->attach_state & PERF_ATTACH_TASK)
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jump_label_dec_deferred(&perf_sched_events);
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static_key_slow_dec_deferred(&perf_sched_events);
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if (event->attr.mmap || event->attr.mmap_data)
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atomic_dec(&nr_mmap_events);
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if (event->attr.comm)
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@@ -2780,7 +2780,7 @@ static void free_event(struct perf_event *event)
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put_callchain_buffers();
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if (is_cgroup_event(event)) {
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atomic_dec(&per_cpu(perf_cgroup_events, event->cpu));
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jump_label_dec_deferred(&perf_sched_events);
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static_key_slow_dec_deferred(&perf_sched_events);
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}
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}
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@@ -4982,7 +4982,7 @@ fail:
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return err;
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}
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struct jump_label_key perf_swevent_enabled[PERF_COUNT_SW_MAX];
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struct static_key perf_swevent_enabled[PERF_COUNT_SW_MAX];
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static void sw_perf_event_destroy(struct perf_event *event)
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{
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@@ -4990,7 +4990,7 @@ static void sw_perf_event_destroy(struct perf_event *event)
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WARN_ON(event->parent);
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jump_label_dec(&perf_swevent_enabled[event_id]);
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static_key_slow_dec(&perf_swevent_enabled[event_id]);
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swevent_hlist_put(event);
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}
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@@ -5020,7 +5020,7 @@ static int perf_swevent_init(struct perf_event *event)
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if (err)
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return err;
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jump_label_inc(&perf_swevent_enabled[event_id]);
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static_key_slow_inc(&perf_swevent_enabled[event_id]);
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event->destroy = sw_perf_event_destroy;
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}
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@@ -5843,7 +5843,7 @@ done:
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if (!event->parent) {
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if (event->attach_state & PERF_ATTACH_TASK)
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jump_label_inc(&perf_sched_events.key);
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static_key_slow_inc(&perf_sched_events.key);
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if (event->attr.mmap || event->attr.mmap_data)
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atomic_inc(&nr_mmap_events);
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if (event->attr.comm)
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@@ -6081,7 +6081,7 @@ SYSCALL_DEFINE5(perf_event_open,
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* - that may need work on context switch
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*/
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atomic_inc(&per_cpu(perf_cgroup_events, event->cpu));
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jump_label_inc(&perf_sched_events.key);
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static_key_slow_inc(&perf_sched_events.key);
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}
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/*
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