1 files changed, 10 insertions, 12 deletions

diff --git a/include/linux/perf_counter.h b/include/linux/perf_counter.h
index 90cce0c74a03..f2b914de3f0c 100644
--- a/include/linux/perf_counter.h
+++ b/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 */