Commit 76e1d904 authored by Frederic Weisbecker's avatar Frederic Weisbecker
Browse files

perf: Store active software events in a hashlist 



Each time a software event triggers, we need to walk through
the entire list of events from the current cpu and task contexts
to retrieve a running perf event that matches.
We also need to check a matching perf event is actually counting.

This walk is wasteful and makes the event fast path scaling
down with a growing number of events running on the same
contexts.

To solve this, we store the running perf events in a hashlist to
get an immediate access to them against their type:event_id when
they trigger.

v2: - Fix SWEVENT_HLIST_SIZE definition (and re-learn some basic
      maths along the way)
    - Only allocate hlist for online cpus, but keep track of the
      refcount on offline possible cpus too, so that we allocate it
      if needed when it becomes online.
    - Drop the kref use as it's not adapted to our tricks anymore.

v3: - Fix bad refcount check (address instead of value). Thanks to
      Eric Dumazet who spotted this.
    - While exiting cpu, move the hlist release out of the IPI path
      to lock the hlist mutex sanely.

Signed-off-by: default avatarFrederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Ingo Molnar <mingo@elte.hu>
parent c0555642

include/linux/perf_event.h

+12 −0
Original line number Diff line number Diff line
@@ -589,6 +589,14 @@ enum perf_group_flag { 
	PERF_GROUP_SOFTWARE = 0x1,

};



#define SWEVENT_HLIST_BITS	8

#define SWEVENT_HLIST_SIZE	(1 << SWEVENT_HLIST_BITS)



struct swevent_hlist {

	struct hlist_head	heads[SWEVENT_HLIST_SIZE];

	struct rcu_head		rcu_head;

};



/**

 * struct perf_event - performance event kernel representation:

 */
@@ -597,6 +605,7 @@ struct perf_event { 
	struct list_head		group_entry;

	struct list_head		event_entry;

	struct list_head		sibling_list;

	struct hlist_node		hlist_entry;

	int				nr_siblings;

	int				group_flags;

	struct perf_event		*group_leader;
@@ -744,6 +753,9 @@ struct perf_cpu_context { 
	int				active_oncpu;

	int				max_pertask;

	int				exclusive;

	struct swevent_hlist		*swevent_hlist;

	struct mutex			hlist_mutex;

	int				hlist_refcount;



	/*

	 * Recursion avoidance:

kernel/perf_event.c

+183 −63
Original line number Diff line number Diff line
@@ -16,6 +16,7 @@ 
#include <linux/file.h>

#include <linux/poll.h>

#include <linux/slab.h>

#include <linux/hash.h>

#include <linux/sysfs.h>

#include <linux/dcache.h>

#include <linux/percpu.h>
@@ -3966,36 +3967,6 @@ static void perf_swevent_add(struct perf_event *event, u64 nr, 
	perf_swevent_overflow(event, 0, nmi, data, regs);

}



static int perf_swevent_is_counting(struct perf_event *event)

{

	/*

	 * The event is active, we're good!

	 */

	if (event->state == PERF_EVENT_STATE_ACTIVE)

		return 1;



	/*

	 * The event is off/error, not counting.

	 */

	if (event->state != PERF_EVENT_STATE_INACTIVE)

		return 0;



	/*

	 * The event is inactive, if the context is active

	 * we're part of a group that didn't make it on the 'pmu',

	 * not counting.

	 */

	if (event->ctx->is_active)

		return 0;



	/*

	 * We're inactive and the context is too, this means the

	 * task is scheduled out, we're counting events that happen

	 * to us, like migration events.

	 */

	return 1;

}



static int perf_tp_event_match(struct perf_event *event,

				struct perf_sample_data *data);
@@ -4019,12 +3990,6 @@ static int perf_swevent_match(struct perf_event *event, 
				struct perf_sample_data *data,

				struct pt_regs *regs)

{

	if (event->cpu != -1 && event->cpu != smp_processor_id())

		return 0;



	if (!perf_swevent_is_counting(event))

		return 0;



	if (event->attr.type != type)

		return 0;
@@ -4041,18 +4006,53 @@ static int perf_swevent_match(struct perf_event *event, 
	return 1;

}



static void perf_swevent_ctx_event(struct perf_event_context *ctx,

				     enum perf_type_id type,

				     u32 event_id, u64 nr, int nmi,

static inline u64 swevent_hash(u64 type, u32 event_id)

{

	u64 val = event_id | (type << 32);



	return hash_64(val, SWEVENT_HLIST_BITS);

}



static struct hlist_head *

find_swevent_head(struct perf_cpu_context *ctx, u64 type, u32 event_id)

{

	u64 hash;

	struct swevent_hlist *hlist;



	hash = swevent_hash(type, event_id);



	hlist = rcu_dereference(ctx->swevent_hlist);

	if (!hlist)

		return NULL;



	return &hlist->heads[hash];

}



static void do_perf_sw_event(enum perf_type_id type, u32 event_id,

				    u64 nr, int nmi,

				    struct perf_sample_data *data,

				    struct pt_regs *regs)

{

	struct perf_cpu_context *cpuctx;

	struct perf_event *event;

	struct hlist_node *node;

	struct hlist_head *head;



	list_for_each_entry_rcu(event, &ctx->event_list, event_entry) {

	cpuctx = &__get_cpu_var(perf_cpu_context);



	rcu_read_lock();



	head = find_swevent_head(cpuctx, type, event_id);



	if (!head)

		goto end;



	hlist_for_each_entry_rcu(event, node, head, hlist_entry) {

		if (perf_swevent_match(event, type, event_id, data, regs))

			perf_swevent_add(event, nr, nmi, data, regs);

	}

end:

	rcu_read_unlock();

}



int perf_swevent_get_recursion_context(void)
@@ -4090,27 +4090,6 @@ void perf_swevent_put_recursion_context(int rctx) 
}

EXPORT_SYMBOL_GPL(perf_swevent_put_recursion_context);



static void do_perf_sw_event(enum perf_type_id type, u32 event_id,

				    u64 nr, int nmi,

				    struct perf_sample_data *data,

				    struct pt_regs *regs)

{

	struct perf_cpu_context *cpuctx;

	struct perf_event_context *ctx;



	cpuctx = &__get_cpu_var(perf_cpu_context);

	rcu_read_lock();

	perf_swevent_ctx_event(&cpuctx->ctx, type, event_id,

				 nr, nmi, data, regs);

	/*

	 * doesn't really matter which of the child contexts the

	 * events ends up in.

	 */

	ctx = rcu_dereference(current->perf_event_ctxp);

	if (ctx)

		perf_swevent_ctx_event(ctx, type, event_id, nr, nmi, data, regs);

	rcu_read_unlock();

}



void __perf_sw_event(u32 event_id, u64 nr, int nmi,

			    struct pt_regs *regs, u64 addr)
@@ -4136,16 +4115,28 @@ static void perf_swevent_read(struct perf_event *event) 
static int perf_swevent_enable(struct perf_event *event)

{

	struct hw_perf_event *hwc = &event->hw;

	struct perf_cpu_context *cpuctx;

	struct hlist_head *head;



	cpuctx = &__get_cpu_var(perf_cpu_context);



	if (hwc->sample_period) {

		hwc->last_period = hwc->sample_period;

		perf_swevent_set_period(event);

	}



	head = find_swevent_head(cpuctx, event->attr.type, event->attr.config);

	if (WARN_ON_ONCE(!head))

		return -EINVAL;



	hlist_add_head_rcu(&event->hlist_entry, head);



	return 0;

}



static void perf_swevent_disable(struct perf_event *event)

{

	hlist_del_rcu(&event->hlist_entry);

}



static const struct pmu perf_ops_generic = {
@@ -4359,13 +4350,115 @@ static int perf_tp_event_match(struct perf_event *event, 
	return 0;

}



static void swevent_hlist_release_rcu(struct rcu_head *rcu_head)

{

	struct swevent_hlist *hlist;



	hlist = container_of(rcu_head, struct swevent_hlist, rcu_head);

	kfree(hlist);

}



static void swevent_hlist_release(struct perf_cpu_context *cpuctx)

{

	struct swevent_hlist *hlist;



	if (!cpuctx->swevent_hlist)

		return;



	hlist = cpuctx->swevent_hlist;

	rcu_assign_pointer(cpuctx->swevent_hlist, NULL);

	call_rcu(&hlist->rcu_head, swevent_hlist_release_rcu);

}



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

{

	struct perf_cpu_context *cpuctx = &per_cpu(perf_cpu_context, cpu);



	mutex_lock(&cpuctx->hlist_mutex);



	if (!--cpuctx->hlist_refcount)

		swevent_hlist_release(cpuctx);



	mutex_unlock(&cpuctx->hlist_mutex);

}



static void swevent_hlist_put(struct perf_event *event)

{

	int cpu;



	if (event->cpu != -1) {

		swevent_hlist_put_cpu(event, event->cpu);

		return;

	}



	for_each_possible_cpu(cpu)

		swevent_hlist_put_cpu(event, cpu);

}



static int swevent_hlist_get_cpu(struct perf_event *event, int cpu)

{

	struct perf_cpu_context *cpuctx = &per_cpu(perf_cpu_context, cpu);

	int err = 0;



	mutex_lock(&cpuctx->hlist_mutex);



	if (!cpuctx->swevent_hlist && cpu_online(cpu)) {

		struct swevent_hlist *hlist;



		hlist = kzalloc(sizeof(*hlist), GFP_KERNEL);

		if (!hlist) {

			err = -ENOMEM;

			goto exit;

		}

		rcu_assign_pointer(cpuctx->swevent_hlist, hlist);

	}

	cpuctx->hlist_refcount++;

 exit:

	mutex_unlock(&cpuctx->hlist_mutex);



	return err;

}



static int swevent_hlist_get(struct perf_event *event)

{

	int err;

	int cpu, failed_cpu;



	if (event->cpu != -1)

		return swevent_hlist_get_cpu(event, event->cpu);



	get_online_cpus();

	for_each_possible_cpu(cpu) {

		err = swevent_hlist_get_cpu(event, cpu);

		if (err) {

			failed_cpu = cpu;

			goto fail;

		}

	}

	put_online_cpus();



	return 0;

 fail:

	for_each_possible_cpu(cpu) {

		if (cpu == failed_cpu)

			break;

		swevent_hlist_put_cpu(event, cpu);

	}



	put_online_cpus();

	return err;

}



static void tp_perf_event_destroy(struct perf_event *event)

{

	perf_trace_disable(event->attr.config);

	swevent_hlist_put(event);

}



static const struct pmu *tp_perf_event_init(struct perf_event *event)

{

	int err;



	/*

	 * Raw tracepoint data is a severe data leak, only allow root to

	 * have these.
@@ -4379,6 +4472,11 @@ static const struct pmu *tp_perf_event_init(struct perf_event *event) 
		return NULL;



	event->destroy = tp_perf_event_destroy;

	err = swevent_hlist_get(event);

	if (err) {

		perf_trace_disable(event->attr.config);

		return ERR_PTR(err);

	}



	return &perf_ops_generic;

}
@@ -4479,6 +4577,7 @@ static void sw_perf_event_destroy(struct perf_event *event) 
	WARN_ON(event->parent);



	atomic_dec(&perf_swevent_enabled[event_id]);

	swevent_hlist_put(event);

}



static const struct pmu *sw_perf_event_init(struct perf_event *event)
@@ -4517,6 +4616,12 @@ static const struct pmu *sw_perf_event_init(struct perf_event *event) 
	case PERF_COUNT_SW_ALIGNMENT_FAULTS:

	case PERF_COUNT_SW_EMULATION_FAULTS:

		if (!event->parent) {

			int err;



			err = swevent_hlist_get(event);

			if (err)

				return ERR_PTR(err);



			atomic_inc(&perf_swevent_enabled[event_id]);

			event->destroy = sw_perf_event_destroy;

		}
@@ -5389,6 +5494,7 @@ static void __init perf_event_init_all_cpus(void) 


	for_each_possible_cpu(cpu) {

		cpuctx = &per_cpu(perf_cpu_context, cpu);

		mutex_init(&cpuctx->hlist_mutex);

		__perf_event_init_context(&cpuctx->ctx, NULL);

	}

}
@@ -5402,6 +5508,16 @@ static void __cpuinit perf_event_init_cpu(int cpu) 
	spin_lock(&perf_resource_lock);

	cpuctx->max_pertask = perf_max_events - perf_reserved_percpu;

	spin_unlock(&perf_resource_lock);



	mutex_lock(&cpuctx->hlist_mutex);

	if (cpuctx->hlist_refcount > 0) {

		struct swevent_hlist *hlist;



		hlist = kzalloc(sizeof(*hlist), GFP_KERNEL);

		WARN_ON_ONCE(!hlist);

		rcu_assign_pointer(cpuctx->swevent_hlist, hlist);

	}

	mutex_unlock(&cpuctx->hlist_mutex);

}



#ifdef CONFIG_HOTPLUG_CPU
@@ -5421,6 +5537,10 @@ static void perf_event_exit_cpu(int cpu) 
	struct perf_cpu_context *cpuctx = &per_cpu(perf_cpu_context, cpu);

	struct perf_event_context *ctx = &cpuctx->ctx;



	mutex_lock(&cpuctx->hlist_mutex);

	swevent_hlist_release(cpuctx);

	mutex_unlock(&cpuctx->hlist_mutex);



	mutex_lock(&ctx->mutex);

	smp_call_function_single(cpu, __perf_event_exit_cpu, NULL, 1);

	mutex_unlock(&ctx->mutex);

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