Commit f2fb6bef authored by Kan Liang's avatar Kan Liang Committed by Ingo Molnar
Browse files

perf/core: Optimize side-band event delivery 



The perf_event_aux() function iterates all PMUs and all events in
their respective per-CPU contexts to find the events to deliver
side-band records to.

For example, the brk test case in lkp triggers many mmap() operations,
which, if we're also running perf, results in many perf_event_aux()
invocations.

If we enable uncore PMU support (even when uncore events are not used),
dozens of uncore PMUs will be iterated, which can significantly
decrease brk_test's throughput.

For example, the brk throughput:

  without uncore PMUs: 2647573 ops_per_sec
  with    uncore PMUs: 1768444 ops_per_sec

... a 33% reduction.

To get at the per-CPU events that need side-band records, this patch
puts these events on a per-CPU list, this avoids iterating the PMUs
and any events that do not need side-band records.

Per task events are unchanged to avoid extra overhead on the context
switch paths.

Suggested-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reported-by: default avatarHuang, Ying <ying.huang@linux.intel.com>
Signed-off-by: default avatarKan Liang <kan.liang@intel.com>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Vince Weaver <vincent.weaver@maine.edu>
Link: http://lkml.kernel.org/r/1458757477-3781-1-git-send-email-kan.liang@intel.com


Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 42c4fb77

include/linux/perf_event.h

+6 −0
Original line number Diff line number Diff line
@@ -517,6 +517,11 @@ struct swevent_hlist { 
struct perf_cgroup;

struct ring_buffer;



struct pmu_event_list {

	raw_spinlock_t		lock;

	struct list_head	list;

};



/**

 * struct perf_event - performance event kernel representation:

 */
@@ -675,6 +680,7 @@ struct perf_event { 
	int				cgrp_defer_enabled;

#endif



	struct list_head		sb_list;

#endif /* CONFIG_PERF_EVENTS */

};

kernel/events/core.c

+73 −12
Original line number Diff line number Diff line
@@ -335,6 +335,7 @@ static atomic_t perf_sched_count; 


static DEFINE_PER_CPU(atomic_t, perf_cgroup_events);

static DEFINE_PER_CPU(int, perf_sched_cb_usages);

static DEFINE_PER_CPU(struct pmu_event_list, pmu_sb_events);



static atomic_t nr_mmap_events __read_mostly;

static atomic_t nr_comm_events __read_mostly;
@@ -3665,6 +3666,26 @@ static void free_event_rcu(struct rcu_head *head) 
static void ring_buffer_attach(struct perf_event *event,

			       struct ring_buffer *rb);



static void detach_sb_event(struct perf_event *event)

{

	struct pmu_event_list *pel = per_cpu_ptr(&pmu_sb_events, event->cpu);



	raw_spin_lock(&pel->lock);

	list_del_rcu(&event->sb_list);

	raw_spin_unlock(&pel->lock);

}



static void unaccount_pmu_sb_event(struct perf_event *event)

{

	if (event->parent)

		return;



	if (event->attach_state & PERF_ATTACH_TASK)

		return;



	detach_sb_event(event);

}



static void unaccount_event_cpu(struct perf_event *event, int cpu)

{

	if (event->parent)
@@ -3728,6 +3749,8 @@ static void unaccount_event(struct perf_event *event) 
	}



	unaccount_event_cpu(event, event->cpu);



	unaccount_pmu_sb_event(event);

}



static void perf_sched_delayed(struct work_struct *work)
@@ -5888,13 +5911,25 @@ perf_event_aux_task_ctx(perf_event_aux_output_cb output, void *data, 
	rcu_read_unlock();

}



static void perf_event_sb_iterate(perf_event_aux_output_cb output, void *data)

{

	struct pmu_event_list *pel = this_cpu_ptr(&pmu_sb_events);

	struct perf_event *event;



	list_for_each_entry_rcu(event, &pel->list, sb_list) {

		if (event->state < PERF_EVENT_STATE_INACTIVE)

			continue;

		if (!event_filter_match(event))

			continue;

		output(event, data);

	}

}



static void

perf_event_aux(perf_event_aux_output_cb output, void *data,

	       struct perf_event_context *task_ctx)

{

	struct perf_cpu_context *cpuctx;

	struct perf_event_context *ctx;

	struct pmu *pmu;

	int ctxn;



	/*
@@ -5909,20 +5944,15 @@ perf_event_aux(perf_event_aux_output_cb output, void *data, 
	}



	rcu_read_lock();

	list_for_each_entry_rcu(pmu, &pmus, entry) {

		cpuctx = get_cpu_ptr(pmu->pmu_cpu_context);

		if (cpuctx->unique_pmu != pmu)

			goto next;

		perf_event_aux_ctx(&cpuctx->ctx, output, data, false);

		ctxn = pmu->task_ctx_nr;

		if (ctxn < 0)

			goto next;

	preempt_disable();

	perf_event_sb_iterate(output, data);



	for_each_task_context_nr(ctxn) {

		ctx = rcu_dereference(current->perf_event_ctxp[ctxn]);

		if (ctx)

			perf_event_aux_ctx(ctx, output, data, false);

next:

		put_cpu_ptr(pmu->pmu_cpu_context);

	}

	preempt_enable();

	rcu_read_unlock();

}
@@ -8615,6 +8645,32 @@ unlock: 
	return pmu;

}



static void attach_sb_event(struct perf_event *event)

{

	struct pmu_event_list *pel = per_cpu_ptr(&pmu_sb_events, event->cpu);



	raw_spin_lock(&pel->lock);

	list_add_rcu(&event->sb_list, &pel->list);

	raw_spin_unlock(&pel->lock);

}



static void account_pmu_sb_event(struct perf_event *event)

{

	struct perf_event_attr *attr = &event->attr;



	if (event->parent)

		return;



	if (event->attach_state & PERF_ATTACH_TASK)

		return;



	if (attr->mmap || attr->mmap_data || attr->mmap2 ||

	    attr->comm || attr->comm_exec ||

	    attr->task ||

	    attr->context_switch)

		attach_sb_event(event);

}



static void account_event_cpu(struct perf_event *event, int cpu)

{

	if (event->parent)
@@ -8695,6 +8751,8 @@ static void account_event(struct perf_event *event) 
enabled:



	account_event_cpu(event, event->cpu);



	account_pmu_sb_event(event);

}



/*
@@ -10203,6 +10261,9 @@ static void __init perf_event_init_all_cpus(void) 
		swhash = &per_cpu(swevent_htable, cpu);

		mutex_init(&swhash->hlist_mutex);

		INIT_LIST_HEAD(&per_cpu(active_ctx_list, cpu));



		INIT_LIST_HEAD(&per_cpu(pmu_sb_events.list, cpu));

		raw_spin_lock_init(&per_cpu(pmu_sb_events.lock, cpu));

	}

}

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