perf: Optimize perf_output_begin() -- address calculation

[~andy/linux] / kernel / events / ring_buffer.c

diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 6929c5848d4ff5ad19a20d6804d809d45da82396..c52a32fa5592c60ba8ebd26c58a73c2fe7e2e69e 100644 (file)
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -105,8 +105,7 @@ int perf_output_begin(struct perf_output_handle *handle,
 {
        struct ring_buffer *rb;
        unsigned long tail, offset, head;
-       int have_lost;
-       struct perf_sample_data sample_data;
+       int have_lost, page_shift;
        struct {
                struct perf_event_header header;
                u64                      id;
@@ -121,35 +120,26 @@ int perf_output_begin(struct perf_output_handle *handle,
                event = event->parent;
 
        rb = rcu_dereference(event->rb);
-       if (!rb)
+       if (unlikely(!rb))
                goto out;
 
-       handle->rb      = rb;
-       handle->event   = event;
-
-       if (!rb->nr_pages)
+       if (unlikely(!rb->nr_pages))
                goto out;
 
+       handle->rb    = rb;
+       handle->event = event;
+
        have_lost = local_read(&rb->lost);
-       if (have_lost) {
-               lost_event.header.size = sizeof(lost_event);
-               perf_event_header__init_id(&lost_event.header, &sample_data,
-                                          event);
-               size += lost_event.header.size;
+       if (unlikely(have_lost)) {
+               size += sizeof(lost_event);
+               if (event->attr.sample_id_all)
+                       size += event->id_header_size;
        }
 
        perf_output_get_handle(handle);
 
        do {
-               /*
-                * Userspace could choose to issue a mb() before updating the
-                * tail pointer. So that all reads will be completed before the
-                * write is issued.
-                *
-                * See perf_output_put_handle().
-                */
                tail = ACCESS_ONCE(rb->user_page->data_tail);
-               smp_mb();
                offset = head = local_read(&rb->head);
                if (!rb->overwrite &&
                    unlikely(CIRC_SPACE(head, tail, perf_data_size(rb)) < size))
@@ -157,22 +147,36 @@ int perf_output_begin(struct perf_output_handle *handle,
                head += size;
        } while (local_cmpxchg(&rb->head, offset, head) != offset);
 
-       if (head - local_read(&rb->wakeup) > rb->watermark)
+       /*
+        * Separate the userpage->tail read from the data stores below.
+        * Matches the MB userspace SHOULD issue after reading the data
+        * and before storing the new tail position.
+        *
+        * See perf_output_put_handle().
+        */
+       smp_mb();
+
+       if (unlikely(head - local_read(&rb->wakeup) > rb->watermark))
                local_add(rb->watermark, &rb->wakeup);
 
-       handle->page = offset >> (PAGE_SHIFT + page_order(rb));
-       handle->page &= rb->nr_pages - 1;
-       handle->size = offset & ((PAGE_SIZE << page_order(rb)) - 1);
-       handle->addr = rb->data_pages[handle->page];
-       handle->addr += handle->size;
-       handle->size = (PAGE_SIZE << page_order(rb)) - handle->size;
+       page_shift = PAGE_SHIFT + page_order(rb);
+
+       handle->page = (offset >> page_shift) & (rb->nr_pages - 1);
+       offset &= (1UL << page_shift) - 1;
+       handle->addr = rb->data_pages[handle->page] + offset;
+       handle->size = (1UL << page_shift) - offset;
 
-       if (have_lost) {
+       if (unlikely(have_lost)) {
+               struct perf_sample_data sample_data;
+
+               lost_event.header.size = sizeof(lost_event);
                lost_event.header.type = PERF_RECORD_LOST;
                lost_event.header.misc = 0;
                lost_event.id          = event->id;
                lost_event.lost        = local_xchg(&rb->lost, 0);
 
+               perf_event_header__init_id(&lost_event.header,
+                                          &sample_data, event);
                perf_output_put(handle, lost_event);
                perf_event__output_id_sample(event, handle, &sample_data);
        }