[PATCH v2 5/5] events: Illustrate the transition to local{,64}_try_cmpxchg

[Uros Bizjak]

This patch illustrates the transition to local{,64}_try_cmpxchg.
It is not intended to be merged as-is.

Signed-off-by: Uros Bizjak <ubiz...@gmail.com>
---
 arch/x86/events/core.c      | 9 ++++-----
 kernel/events/ring_buffer.c | 5 +++--
 2 files changed, 7 insertions(+), 7 deletions(-)

diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c
index d096b04bf80e..d9310e9363f1 100644
--- a/arch/x86/events/core.c
+++ b/arch/x86/events/core.c
@@ -129,13 +129,12 @@ u64 x86_perf_event_update(struct perf_event *event)
         * exchange a new raw count - then add that new-prev delta
         * count to the generic event atomically:
         */
-again:
        prev_raw_count = local64_read(&hwc->prev_count);
-       rdpmcl(hwc->event_base_rdpmc, new_raw_count);
 
-       if (local64_cmpxchg(&hwc->prev_count, prev_raw_count,
-                                       new_raw_count) != prev_raw_count)
-               goto again;
+       do {
+               rdpmcl(hwc->event_base_rdpmc, new_raw_count);
+       } while (!local64_try_cmpxchg(&hwc->prev_count, &prev_raw_count,
+                                     new_raw_count));
 
        /*
         * Now we have the new raw value and have updated the prev
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index 273a0fe7910a..111ab85ee97d 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -191,9 +191,10 @@ __perf_output_begin(struct perf_output_handle *handle,
 
        perf_output_get_handle(handle);
 
+       offset = local_read(&rb->head);
        do {
                tail = READ_ONCE(rb->user_page->data_tail);
-               offset = head = local_read(&rb->head);
+               head = offset;
                if (!rb->overwrite) {
                        if (unlikely(!ring_buffer_has_space(head, tail,
                                                            perf_data_size(rb),
@@ -217,7 +218,7 @@ __perf_output_begin(struct perf_output_handle *handle,
                        head += size;
                else
                        head -= size;
-       } while (local_cmpxchg(&rb->head, offset, head) != offset);
+       } while (!local_try_cmpxchg(&rb->head, &offset, head));
 
        if (backward) {
                offset = head;
-- 
2.39.2