perf_counter: counter overflow limit

Provide means to auto-disable the counter after 'n' overflow events.

Create the counter with hw_event.disabled = 1, and then issue an
ioctl(fd, PREF_COUNTER_IOC_REFRESH, n); to set the limit and enable
the counter.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
LKML-Reference: <20090406094518.083139737@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

2 files changed, 50 insertions, 13 deletions

diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index 928a7fae0961..ef4dcbff75ab 100644
--- a/include/linux/perf_counter.h
+++ b/include/linux/perf_counter.h
@@ -155,8 +155,9 @@ struct perf_counter_hw_event {
 /*
  * Ioctls that can be done on a perf counter fd:
  */
-#define PERF_COUNTER_IOC_ENABLE         _IO('$', 0)
-#define PERF_COUNTER_IOC_DISABLE        _IO('$', 1)
+#define PERF_COUNTER_IOC_ENABLE         _IO ('$', 0)
+#define PERF_COUNTER_IOC_DISABLE        _IO ('$', 1)
+#define PERF_COUNTER_IOC_REFRESH        _IOW('$', 2, u32)
 
 /*
  * Structure of the page that can be mapped via mmap
@@ -403,9 +404,14 @@ struct perf_counter {
         /* poll related */
         wait_queue_head_t               waitq;
         struct fasync_struct            *fasync;
-        /* optional: for NMIs */
+
+        /* delayed work for NMIs and such */
+        int                             pending_wakeup;
+        int                             pending_disable;
         struct perf_pending_entry       pending;
 
+        atomic_t                        event_limit;
+
         void (*destroy)(struct perf_counter *);
         struct rcu_head                 rcu_head;
 #endif
diff --git a/kernel/perf_counter.c b/kernel/perf_counter.c
index 19990d1f0215..c05e10354bc9 100644
--- a/kernel/perf_counter.c
+++ b/kernel/perf_counter.c
@@ -744,6 +744,12 @@ static void perf_counter_enable(struct perf_counter *counter)
         spin_unlock_irq(&ctx->lock);
 }
 
+static void perf_counter_refresh(struct perf_counter *counter, int refresh)
+{
+        atomic_add(refresh, &counter->event_limit);
+        perf_counter_enable(counter);
+}
+
 /*
  * Enable a counter and all its children.
  */
@@ -1311,6 +1317,9 @@ static long perf_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
         case PERF_COUNTER_IOC_DISABLE:
                 perf_counter_disable_family(counter);
                 break;
+        case PERF_COUNTER_IOC_REFRESH:
+                perf_counter_refresh(counter, arg);
+                break;
         default:
                 err = -ENOTTY;
         }
@@ -1590,14 +1599,6 @@ void perf_counter_wakeup(struct perf_counter *counter)
         kill_fasync(&counter->fasync, SIGIO, POLL_IN);
 }
 
-static void perf_pending_wakeup(struct perf_pending_entry *entry)
-{
-        struct perf_counter *counter = container_of(entry,
-                        struct perf_counter, pending);
-
-        perf_counter_wakeup(counter);
-}
-
 /*
  * Pending wakeups
  *
@@ -1607,6 +1608,22 @@ static void perf_pending_wakeup(struct perf_pending_entry *entry)
  * single linked list and use cmpxchg() to add entries lockless.
  */
 
+static void perf_pending_counter(struct perf_pending_entry *entry)
+{
+        struct perf_counter *counter = container_of(entry,
+                        struct perf_counter, pending);
+
+        if (counter->pending_disable) {
+                counter->pending_disable = 0;
+                perf_counter_disable(counter);
+        }
+
+        if (counter->pending_wakeup) {
+                counter->pending_wakeup = 0;
+                perf_counter_wakeup(counter);
+        }
+}
+
 #define PENDING_TAIL ((struct perf_pending_entry *)-1UL)
 
 static DEFINE_PER_CPU(struct perf_pending_entry *, perf_pending_head) = {
@@ -1715,8 +1732,9 @@ struct perf_output_handle {
 static inline void __perf_output_wakeup(struct perf_output_handle *handle)
 {
         if (handle->nmi) {
+                handle->counter->pending_wakeup = 1;
                 perf_pending_queue(&handle->counter->pending,
-                                   perf_pending_wakeup);
+                                   perf_pending_counter);
         } else
                 perf_counter_wakeup(handle->counter);
 }
@@ -2063,8 +2081,21 @@ void perf_counter_munmap(unsigned long addr, unsigned long len,
 int perf_counter_overflow(struct perf_counter *counter,
                           int nmi, struct pt_regs *regs)
 {
+        int events = atomic_read(&counter->event_limit);
+        int ret = 0;
+
+        if (events && atomic_dec_and_test(&counter->event_limit)) {
+                ret = 1;
+                if (nmi) {
+                        counter->pending_disable = 1;
+                        perf_pending_queue(&counter->pending,
+                                           perf_pending_counter);
+                } else
+                        perf_counter_disable(counter);
+        }
+
         perf_counter_output(counter, nmi, regs);
-        return 0;
+        return ret;
 }
 
 /*