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>

diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index 17b63105f2aa79917068725657b99939a6121536..0fcbf34a4f73b047cd5c7b1473ae05ff69c71446 100644 (file)
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -160,6 +160,7 @@ struct perf_counter_hw_event {
 #define PERF_COUNTER_IOC_ENABLE                _IO ('$', 0)
 #define PERF_COUNTER_IOC_DISABLE       _IO ('$', 1)
 #define PERF_COUNTER_IOC_REFRESH       _IOW('$', 2, u32)
+#define PERF_COUNTER_IOC_RESET         _IO ('$', 3)
 
 /*
  * Structure of the page that can be mapped via mmap

diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index ba5e921e1f36db72807b867952306e520880eb9d..6e6834e0587e01238cc950015d635b632038e911 100644 (file)
--- 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;
        }