[PATCH 1/5] perf: Provide a proper stop action for software events

[Frederic Weisbecker <fweisbec@gmail.com>]

In order to introduce new context exclusions, software events will
have to eventually stop when needed. We'll want perf_event_stop() to
act on every events.

To achieve this, remove the stub stop/start pmu callbacks of software
and tracepoint events that fixed a race in perf_adjust_period, and do
an explicit check to only reset the hardware event using the
start/stop callbacks.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Zhang Yanmin <yanmin_zhang@linux.intel.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
---
 kernel/perf_event.c |   30 +++++++++++++++++-------------
 1 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index c772a3d..95a56ed 100644
--- a/kernel/perf_event.c
+++ b/kernel/perf_event.c
@@ -1541,11 +1541,24 @@ static void perf_adjust_period(struct perf_event *event, u64 nsec, u64 count)
 	hwc->sample_period = sample_period;
 
 	if (local64_read(&hwc->period_left) > 8*sample_period) {
-		perf_disable();
-		perf_event_stop(event);
+		bool software_event = is_software_event(event);
+
+		/*
+		 * Only hardware events need their irq period to be
+		 * reprogrammed. And stopping and restarting software
+		 * events here would be dangerously racy.
+		 */
+		if (!software_event) {
+			perf_disable();
+			perf_event_stop(event);
+		}
+
 		local64_set(&hwc->period_left, 0);
-		perf_event_start(event);
-		perf_enable();
+
+		if (!software_event) {
+			perf_event_start(event);
+			perf_enable();
+		}
 	}
 }
 
@@ -4286,16 +4299,9 @@ static void perf_swevent_void(struct perf_event *event)
 {
 }
 
-static int perf_swevent_int(struct perf_event *event)
-{
-	return 0;
-}
-
 static const struct pmu perf_ops_generic = {
 	.enable		= perf_swevent_enable,
 	.disable	= perf_swevent_disable,
-	.start		= perf_swevent_int,
-	.stop		= perf_swevent_void,
 	.read		= perf_swevent_read,
 	.unthrottle	= perf_swevent_void, /* hwc->interrupts already reset */
 };
@@ -4578,8 +4584,6 @@ static int swevent_hlist_get(struct perf_event *event)
 static const struct pmu perf_ops_tracepoint = {
 	.enable		= perf_trace_enable,
 	.disable	= perf_trace_disable,
-	.start		= perf_swevent_int,
-	.stop		= perf_swevent_void,
 	.read		= perf_swevent_read,
 	.unthrottle	= perf_swevent_void,
 };
-- 
1.6.2.3