---

yaml
---
r: 147322
b: refs/heads/master
c: 92f22a3
h: refs/heads/master
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 5872bdb88a35fae7d224bd6b21e5f377e854ccfc
+refs/heads/master: 92f22a3865abe87eea2609a6f8e5be5123f7ce4f

trunk/include/linux/perf_counter.h

@@ -167,30 +167,28 @@ struct perf_counter_mmap_page {
 	/*
 	 * Bits needed to read the hw counters in user-space.
 	 *
-	 * The index and offset should be read atomically using the seqlock:
-	 *
-	 *   __u32 seq, index;
-	 *   __s64 offset;
+	 *   u32 seq;
+	 *   s64 count;
 	 *
 	 * again:
-	 *   rmb();
 	 *   seq = pc->lock;
-	 *
 	 *   if (unlikely(seq & 1)) {
 	 *     cpu_relax();
 	 *     goto again;
 	 *   }
 	 *
-	 *   index = pc->index;
-	 *   offset = pc->offset;
+	 *   if (pc->index) {
+	 *     count = pmc_read(pc->index - 1);
+	 *     count += pc->offset;
+	 *   } else
+	 *     goto regular_read;
 	 *
-	 *   rmb();
+	 *   barrier();
 	 *   if (pc->lock != seq)
 	 *     goto again;
 	 *
-	 * After this, index contains architecture specific counter index + 1,
-	 * so that 0 means unavailable, offset contains the value to be added
-	 * to the result of the raw timer read to obtain this counter's value.
+	 * NOTE: for obvious reason this only works on self-monitoring
+	 *       processes.
 	 */
 	__u32	lock;			/* seqlock for synchronization */
 	__u32	index;			/* hardware counter identifier */

trunk/kernel/perf_counter.c

@@ -1340,13 +1340,13 @@ void perf_counter_update_userpage(struct perf_counter *counter)
 	 */
 	preempt_disable();
 	++userpg->lock;
-	smp_wmb();
+	barrier();
 	userpg->index = counter->hw.idx;
 	userpg->offset = atomic64_read(&counter->count);
 	if (counter->state == PERF_COUNTER_STATE_ACTIVE)
 		userpg->offset -= atomic64_read(&counter->hw.prev_count);
 
-	smp_wmb();
+	barrier();
 	++userpg->lock;
 	preempt_enable();
 unlock: