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Re: [PATCH v3 7/8] perf: Define PMU_TXN_READ interface

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  Re: [PATCH v3 7/8] perf: Define PMU_TXN_READ interface Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com> - 2015-07-23 01:30 +0200
    Re: [PATCH v3 7/8] perf: Define PMU_TXN_READ interface Peter Zijlstra <peterz@infradead.org> - 2015-07-23 10:10 +0200
      Re: [PATCH v3 7/8] perf: Define PMU_TXN_READ interface Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com> - 2015-07-24 03:20 +0200

#1190355 — Re: [PATCH v3 7/8] perf: Define PMU_TXN_READ interface

Peter Zijlstra [peterz@infradead.org] wrote:
| I've not woken up yet, and not actually fully read the email, but can
| you stuff the entire above chunk inside the IPI?
| 
| I think you could then actually optimize __perf_event_read() as well,
| because all these events should be on the same context, so no point in
| calling update_*time*() for every event or so.
| 

Do you mean something like this (will move the rename to a separate
patch before posting):
--

From e8eddb5d3877ebdb3b71213a00aaa980f4010dd0 Mon Sep 17 00:00:00 2001
From: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Date: Tue, 7 Jul 2015 21:45:23 -0400
Subject: [PATCH 1/1] perf: Define PMU_TXN_READ interface

Define a new PERF_PMU_TXN_READ interface to read a group of counters
at once. Note that we use this interface with all PMUs.

PMUs that implement this interface use the ->read() operation to _queue_
the counters to be read and use ->commit_txn() to actually read all the
queued counters at once.

PMUs that don't implement PERF_PMU_TXN_READ ignore ->start_txn() and
->commit_txn() and continue to read counters one at a time.

Thanks to input from Peter Zijlstra.

Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
---

Changelog[v5]
	[Peter Zijlstra] Ensure the entire transaction happens on the same CPU.

Changelog[v4]
	[Peter Zijlstra] Add lockdep_assert_held() in perf_event_read_group()
---
 include/linux/perf_event.h |    1 +
 kernel/events/core.c       |   72 +++++++++++++++++++++++++++++++++++++-------
 2 files changed, 62 insertions(+), 11 deletions(-)

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 44bf05f..da307ad 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -169,6 +169,7 @@ struct perf_event;
 #define PERF_EVENT_TXN 0x1
 
 #define PERF_PMU_TXN_ADD  0x1		/* txn to add/schedule event on PMU */
+#define PERF_PMU_TXN_READ 0x2		/* txn to read event group from PMU */
 
 /**
  * pmu::capabilities flags
diff --git a/kernel/events/core.c b/kernel/events/core.c
index a6bd09d..7177dd8 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3174,12 +3174,8 @@ void perf_event_exec(void)
 	rcu_read_unlock();
 }
 
-/*
- * Cross CPU call to read the hardware event
- */
-static void __perf_event_read(void *info)
+static void __perf_event_read(struct perf_event *event, int update_ctx)
 {
-	struct perf_event *event = info;
 	struct perf_event_context *ctx = event->ctx;
 	struct perf_cpu_context *cpuctx = __get_cpu_context(ctx);
 
@@ -3194,7 +3190,7 @@ static void __perf_event_read(void *info)
 		return;
 
 	raw_spin_lock(&ctx->lock);
-	if (ctx->is_active) {
+	if (ctx->is_active && update_ctx) {
 		update_context_time(ctx);
 		update_cgrp_time_from_event(event);
 	}
@@ -3204,6 +3200,16 @@ static void __perf_event_read(void *info)
 	raw_spin_unlock(&ctx->lock);
 }
 
+/*
+ * Cross CPU call to read the hardware event
+ */
+static void __perf_event_read_ipi(void *info)
+{
+	struct perf_event *event = info;
+
+	__perf_event_read(event, 1);
+}
+
 static inline u64 perf_event_count(struct perf_event *event)
 {
 	if (event->pmu->count)
@@ -3220,7 +3226,7 @@ static void perf_event_read(struct perf_event *event)
 	 */
 	if (event->state == PERF_EVENT_STATE_ACTIVE) {
 		smp_call_function_single(event->oncpu,
-					 __perf_event_read, event, 1);
+					 __perf_event_read_ipi, event, 1);
 	} else if (event->state == PERF_EVENT_STATE_INACTIVE) {
 		struct perf_event_context *ctx = event->ctx;
 		unsigned long flags;
@@ -3765,6 +3771,36 @@ static void orphans_remove_work(struct work_struct *work)
 	put_ctx(ctx);
 }
 
+/*
+ * Use the transaction interface to read the group of events in @leader.
+ * PMUs like the 24x7 counters in Power, can use this to queue the events
+ * in the ->read() operation and perform the actual read in ->commit_txn.
+ *
+ * Other PMUs can ignore the ->start_txn and ->commit_txn and read each
+ * PMU directly in the ->read() operation.
+ */
+static int perf_event_read_group(struct perf_event *leader)
+{
+	int ret;
+	struct perf_event *sub;
+	struct pmu *pmu;
+	struct perf_event_context *ctx = leader->ctx;
+
+	lockdep_assert_held(&ctx->mutex);
+
+	pmu = leader->pmu;
+
+	pmu->start_txn(pmu, PERF_PMU_TXN_READ);
+
+	__perf_event_read(leader, 1);
+	list_for_each_entry(sub, &leader->sibling_list, group_entry)
+		__perf_event_read(sub, 0);
+
+	ret = pmu->commit_txn(pmu);
+
+	return ret;
+}
+
 u64 perf_event_read_value(struct perf_event *event, u64 *enabled, u64 *running)
 {
 	u64 total = 0;
@@ -3794,7 +3830,17 @@ static int perf_read_group(struct perf_event *event,
 
 	lockdep_assert_held(&ctx->mutex);
 
-	count = perf_event_read_value(leader, &enabled, &running);
+	mutex_lock(&leader->child_mutex);
+
+	ret = perf_event_read_group(leader);
+	if (ret) {
+		mutex_unlock(&leader->child_mutex);
+		return ret;
+	}
+
+	count = perf_event_aggregate(leader, &enabled, &running);
+
+	mutex_unlock(&leader->child_mutex);
 
 	values[n++] = 1 + leader->nr_siblings;
 	if (read_format & PERF_FORMAT_TOTAL_TIME_ENABLED)
@@ -3815,15 +3861,19 @@ static int perf_read_group(struct perf_event *event,
 	list_for_each_entry(sub, &leader->sibling_list, group_entry) {
 		n = 0;
 
-		values[n++] = perf_event_read_value(sub, &enabled, &running);
+		mutex_lock(&sub->child_mutex);
+
+		values[n++] = perf_event_aggregate(sub, &enabled, &running);
+
+		mutex_unlock(&sub->child_mutex);
+
 		if (read_format & PERF_FORMAT_ID)
 			values[n++] = primary_event_id(sub);
 
 		size = n * sizeof(u64);
 
-		if (copy_to_user(buf + ret, values, size)) {
+		if (copy_to_user(buf + ret, values, size))
 			return -EFAULT;
-		}
 
 		ret += size;
 	}
-- 
1.7.9.5

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#1190700

On Wed, Jul 22, 2015 at 04:19:16PM -0700, Sukadev Bhattiprolu wrote:
> Peter Zijlstra [peterz@infradead.org] wrote:
> | I've not woken up yet, and not actually fully read the email, but can
> | you stuff the entire above chunk inside the IPI?
> | 
> | I think you could then actually optimize __perf_event_read() as well,
> | because all these events should be on the same context, so no point in
> | calling update_*time*() for every event or so.
> | 
> 
> Do you mean something like this (will move the rename to a separate
> patch before posting):

More like so.. please double check, I've not even had tea yet.

--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3174,14 +3174,22 @@ void perf_event_exec(void)
 	rcu_read_unlock();
 }
 
+struct perf_read_data {
+	struct perf_event *event;
+	bool group;
+	int ret;
+};
+
 /*
  * Cross CPU call to read the hardware event
  */
 static void __perf_event_read(void *info)
 {
-	struct perf_event *event = info;
+	struct perf_read_data *data = info;
+	struct perf_event *sub, *event = data->event;
 	struct perf_event_context *ctx = event->ctx;
 	struct perf_cpu_context *cpuctx = __get_cpu_context(ctx);
+	struct pmu *pmu = event->pmu;
 
 	/*
 	 * If this is a task context, we need to check whether it is
@@ -3199,8 +3207,23 @@ static void __perf_event_read(void *info
 		update_cgrp_time_from_event(event);
 	}
 	update_event_times(event);
-	if (event->state == PERF_EVENT_STATE_ACTIVE)
-		event->pmu->read(event);
+	if (event->state != PERF_EVENT_STATE_ACTIVE)
+		goto unlock;
+
+	if (!data->group) {
+		pmu->read(event);
+		goto unlock;
+	}
+
+	pmu->start_txn(pmu, PERF_PMU_TXN_READ);
+	pmu->read(event);
+	list_for_each_entry(sub, &event->sibling_list, group_entry) {
+		if (sub->state == PERF_EVENT_STATE_ACTIVE)
+			pmu->read(sub);
+	}
+	data->ret = pmu->commit_txn(pmu);
+
+unlock:
 	raw_spin_unlock(&ctx->lock);
 }
 
@@ -3212,15 +3235,23 @@ static inline u64 perf_event_count(struc
 	return __perf_event_count(event);
 }
 
-static void perf_event_read(struct perf_event *event)
+static int perf_event_read(struct perf_event *event, bool group)
 {
+	int ret = 0
+
 	/*
 	 * If event is enabled and currently active on a CPU, update the
 	 * value in the event structure:
 	 */
 	if (event->state == PERF_EVENT_STATE_ACTIVE) {
+		struct perf_read_data data = {
+			.event = event,
+			.group = group,
+			.ret = 0,
+		};
 		smp_call_function_single(event->oncpu,
-					 __perf_event_read, event, 1);
+					 __perf_event_read, &data, 1);
+		ret = data.ret;
 	} else if (event->state == PERF_EVENT_STATE_INACTIVE) {
 		struct perf_event_context *ctx = event->ctx;
 		unsigned long flags;
@@ -3235,9 +3266,14 @@ static void perf_event_read(struct perf_
 			update_context_time(ctx);
 			update_cgrp_time_from_event(event);
 		}
-		update_event_times(event);
+		if (group)
+			update_group_times(event);
+		else
+			update_event_times(event);
 		raw_spin_unlock_irqrestore(&ctx->lock, flags);
 	}
+
+	return ret;
 }
 
 /*
@@ -3718,7 +3754,6 @@ static u64 perf_event_compute(struct per
 			atomic64_read(&event->child_total_time_running);
 
 	list_for_each_entry(child, &event->child_list, child_list) {
-		perf_event_read(child);
 		total += perf_event_count(child);
 		*enabled += child->total_time_enabled;
 		*running += child->total_time_running;
@@ -3772,7 +3807,7 @@ u64 perf_event_read_value(struct perf_ev
 
 	mutex_lock(&event->child_mutex);
 
-	perf_event_read(event);
+	perf_event_read(event, false);
 	total = perf_event_compute(event, enabled, running);
 
 	mutex_unlock(&event->child_mutex);
@@ -3792,7 +3827,11 @@ static int perf_read_group(struct perf_e
 
 	lockdep_assert_held(&ctx->mutex);
 
-	count = perf_event_read_value(leader, &enabled, &running);
+	ret = perf_event_read(leader, true);
+	if (ret)
+		return ret;
+
+	count = perf_event_compute(leader, &enabled, &running);
 
 	values[n++] = 1 + leader->nr_siblings;
 	if (read_format & PERF_FORMAT_TOTAL_TIME_ENABLED)
@@ -3813,7 +3852,7 @@ static int perf_read_group(struct perf_e
 	list_for_each_entry(sub, &leader->sibling_list, group_entry) {
 		n = 0;
 
-		values[n++] = perf_event_read_value(sub, &enabled, &running);
+		values[n++] = perf_event_compute(sub, &enabled, &running);
 		if (read_format & PERF_FORMAT_ID)
 			values[n++] = primary_event_id(sub);
 
@@ -3931,7 +3970,7 @@ static unsigned int perf_poll(struct fil
 
 static void _perf_event_reset(struct perf_event *event)
 {
-	perf_event_read(event);
+	perf_event_read(event, false);
 	local64_set(&event->count, 0);
 	perf_event_update_userpage(event);
 }
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#1191416

Peter Zijlstra [peterz@infradead.org] wrote:
| On Wed, Jul 22, 2015 at 04:19:16PM -0700, Sukadev Bhattiprolu wrote:
| > Peter Zijlstra [peterz@infradead.org] wrote:
| > | I've not woken up yet, and not actually fully read the email, but can
| > | you stuff the entire above chunk inside the IPI?
| > | 
| > | I think you could then actually optimize __perf_event_read() as well,
| > | because all these events should be on the same context, so no point in
| > | calling update_*time*() for every event or so.
| > | 
| > 
| > Do you mean something like this (will move the rename to a separate
| > patch before posting):
| 
| More like so.. please double check, I've not even had tea yet.

Yeah, I realized I had ignored the 'event->cpu' spec.
Will try this out. Thanks,

Sukadev

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