perf_counter: add ioctl(PERF_COUNTER_IOC_RESET)

Provide a way to reset an existing counter - this eases PAPI
libraries around perfcounters.

Similar to read() it doesn't collapse pending child counters.

[ Impact: new perfcounter fd ioctl method to reset counters ]

Suggested-by: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
LKML-Reference: <20090505155437.022272933@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 8 insertions, 0 deletions

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index ba5e921e1f36..6e6834e0587e 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -1288,6 +1288,11 @@ static unsigned int perf_poll(struct file *file, poll_table *wait)
         return events;
 }
 
+static void perf_counter_reset(struct perf_counter *counter)
+{
+        atomic_set(&counter->count, 0);
+}
+
 static long perf_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 {
         struct perf_counter *counter = file->private_data;
@@ -1303,6 +1308,9 @@ static long perf_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
         case PERF_COUNTER_IOC_REFRESH:
                 perf_counter_refresh(counter, arg);
                 break;
+        case PERF_COUNTER_IOC_RESET:
+                perf_counter_reset(counter);
+                break;
         default:
                 err = -ENOTTY;
         }