perf_counter: Add ioctl for changing the sample period/frequency

Reported-by: Stephane Eranian <eranian@googlemail.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: John Kacur <jkacur@redhat.com>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 46 insertions, 4 deletions

diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index c046f7d97cfa..45bdd3b95d3e 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -164,10 +164,11 @@ struct perf_counter_hw_event {
 /*
  * Ioctls that can be done on a perf counter fd:
  */
-#define PERF_COUNTER_IOC_ENABLE         _IOW('$', 0, u32)
-#define PERF_COUNTER_IOC_DISABLE        _IOW('$', 1, u32)
-#define PERF_COUNTER_IOC_REFRESH        _IOW('$', 2, u32)
-#define PERF_COUNTER_IOC_RESET          _IOW('$', 3, u32)
+#define PERF_COUNTER_IOC_ENABLE         _IO ('$', 0)
+#define PERF_COUNTER_IOC_DISABLE        _IO ('$', 1)
+#define PERF_COUNTER_IOC_REFRESH        _IO ('$', 2)
+#define PERF_COUNTER_IOC_RESET          _IO ('$', 3)
+#define PERF_COUNTER_IOC_PERIOD         _IOW('$', 4, u64)
 
 enum perf_counter_ioc_flags {
         PERF_IOC_FLAG_GROUP             = 1U << 0,
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 3f11a2bc6c79..abe2f3b6c424 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -1604,6 +1604,43 @@ static void perf_counter_for_each(struct perf_counter *counter,
         mutex_unlock(&counter->child_mutex);
 }
 
+static int perf_counter_period(struct perf_counter *counter, u64 __user *arg)
+{
+        struct perf_counter_context *ctx = counter->ctx;
+        unsigned long size;
+        int ret = 0;
+        u64 value;
+
+        if (!counter->hw_event.sample_period)
+                return -EINVAL;
+
+        size = copy_from_user(&value, arg, sizeof(value));
+        if (size != sizeof(value))
+                return -EFAULT;
+
+        if (!value)
+                return -EINVAL;
+
+        spin_lock_irq(&ctx->lock);
+        if (counter->hw_event.freq) {
+                if (value > sysctl_perf_counter_limit) {
+                        ret = -EINVAL;
+                        goto unlock;
+                }
+
+                counter->hw_event.sample_freq = value;
+        } else {
+                counter->hw_event.sample_period = value;
+                counter->hw.sample_period = value;
+
+                perf_log_period(counter, value);
+        }
+unlock:
+        spin_unlock_irq(&ctx->lock);
+
+        return ret;
+}
+
 static long perf_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 {
         struct perf_counter *counter = file->private_data;
@@ -1623,6 +1660,10 @@ static long perf_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
 
         case PERF_COUNTER_IOC_REFRESH:
                 return perf_counter_refresh(counter, arg);
+
+        case PERF_COUNTER_IOC_PERIOD:
+                return perf_counter_period(counter, (u64 __user *)arg);
+
         default:
                 return -ENOTTY;
         }