linux-kernel - [PATCH v3 4/8] perf: Split perf_event_read() and perf_event

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Date:	Tue, 14 Jul 2015 20:01:51 -0700
From:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Michael Ellerman <mpe@...erman.id.au>
Cc:	<linux-kernel@...r.kernel.org>, linuxppc-dev@...ts.ozlabs.org,
	linux-s390@...r.kernel.org, sparclinux@...r.kernel.org
Subject: [PATCH v3 4/8] perf: Split perf_event_read() and perf_event_count()

perf_event_read() does two things:

	- call the PMU to read/update the counter value, and
	- compute the total count of the event and its children

Not all callers need both. perf_event_reset() for instance needs the
first piece but doesn't need the second.  Similarly, when we implement
the ability to read a group of events using the transaction interface,
we would need the two pieces done independently.

Break up perf_event_read() and have it just read/update the counter
and have the callers compute the total count if necessary.

Signed-off-by: Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
---
 kernel/events/core.c |   14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index b79aad2..44fb89d 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3212,7 +3212,7 @@ static inline u64 perf_event_count(struct perf_event *event)
 	return __perf_event_count(event);
 }
 
-static u64 perf_event_read(struct perf_event *event)
+static void perf_event_read(struct perf_event *event)
 {
 	/*
 	 * If event is enabled and currently active on a CPU, update the
@@ -3238,8 +3238,6 @@ static u64 perf_event_read(struct perf_event *event)
 		update_event_times(event);
 		raw_spin_unlock_irqrestore(&ctx->lock, flags);
 	}
-
-	return perf_event_count(event);
 }
 
 /*
@@ -3751,14 +3749,18 @@ u64 perf_event_read_value(struct perf_event *event, u64 *enabled, u64 *running)
 	*running = 0;
 
 	mutex_lock(&event->child_mutex);
-	total += perf_event_read(event);
+
+	perf_event_read(event);
+	total += perf_event_count(event);
+
 	*enabled += event->total_time_enabled +
 			atomic64_read(&event->child_total_time_enabled);
 	*running += event->total_time_running +
 			atomic64_read(&event->child_total_time_running);
 
 	list_for_each_entry(child, &event->child_list, child_list) {
-		total += perf_event_read(child);
+		perf_event_read(child);
+		total += perf_event_count(child);
 		*enabled += child->total_time_enabled;
 		*running += child->total_time_running;
 	}
@@ -3918,7 +3920,7 @@ static unsigned int perf_poll(struct file *file, poll_table *wait)
 
 static void _perf_event_reset(struct perf_event *event)
 {
-	(void)perf_event_read(event);
+	perf_event_read(event);
 	local64_set(&event->count, 0);
 	perf_event_update_userpage(event);
 }
-- 
1.7.9.5

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