perf/core: Provide a kernel-internal interface to pause perf_event

Exporting perf_event_pause() as an external accessor for kernel users (such
as KVM) who may do both disable perf_event and read count with just one
time to hold perf_event_ctx_lock. Also the value could be reset optionally.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Like Xu <like.xu@linux.intel.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index d601df3..e9768bf 100644 (file)
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1337,6 +1337,7 @@ extern void perf_event_disable_inatomic(struct perf_event *event);
 extern void perf_event_task_tick(void);
 extern int perf_event_account_interrupt(struct perf_event *event);
 extern int perf_event_period(struct perf_event *event, u64 value);
+extern u64 perf_event_pause(struct perf_event *event, bool reset);
 #else /* !CONFIG_PERF_EVENTS: */
 static inline void *
 perf_aux_output_begin(struct perf_output_handle *handle,
@@ -1420,6 +1421,10 @@ static inline int perf_event_period(struct perf_event *event, u64 value)
 {
        return -EINVAL;
 }
+static inline u64 perf_event_pause(struct perf_event *event, bool reset)
+{
+       return 0;
+}
 #endif
 
 #if defined(CONFIG_PERF_EVENTS) && defined(CONFIG_CPU_SUP_INTEL)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index e1b83d2..fc9f5eb 100644 (file)
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5029,6 +5029,24 @@ static void _perf_event_reset(struct perf_event *event)
        perf_event_update_userpage(event);
 }
 
+/* Assume it's not an event with inherit set. */
+u64 perf_event_pause(struct perf_event *event, bool reset)
+{
+       struct perf_event_context *ctx;
+       u64 count;
+
+       ctx = perf_event_ctx_lock(event);
+       WARN_ON_ONCE(event->attr.inherit);
+       _perf_event_disable(event);
+       count = local64_read(&event->count);
+       if (reset)
+               local64_set(&event->count, 0);
+       perf_event_ctx_unlock(event, ctx);
+
+       return count;
+}
+EXPORT_SYMBOL_GPL(perf_event_pause);
+
 /*
  * Holding the top-level event's child_mutex means that any
  * descendant process that has inherited this event will block