Will Deacon <will.dea...@arm.com> writes:
> The aux_head and aux_wakeup members of struct ring_buffer are defined
> using the local_t type, despite the fact that they are only accessed via
> the perf_aux_output_* functions, which cannot race with each other for a
> given ring buffer.
>
> This patch changes the type of the members to long, so we can avoid
> using the local_* API where it isn't needed.
Thanks for digging this up! Some minor nits below.
> @@ -434,12 +434,12 @@ void perf_aux_output_end(struct perf_output_handle
> *handle, unsigned long size)
> handle->aux_flags |= PERF_AUX_FLAG_OVERWRITE;
>
> aux_head = handle->head;
> - local_set(&rb->aux_head, aux_head);
> + rb->aux_head = aux_head;
> } else {
> handle->aux_flags &= ~PERF_AUX_FLAG_OVERWRITE;
>
> - aux_head = local_read(&rb->aux_head);
> - local_add(size, &rb->aux_head);
> + aux_head = rb->aux_head;
> + rb->aux_head += size;
> }
>
> if (size || handle->aux_flags) {
> @@ -451,11 +451,11 @@ void perf_aux_output_end(struct perf_output_handle
> *handle, unsigned long size)
> handle->aux_flags);
> }
>
> - aux_head = rb->user_page->aux_head = local_read(&rb->aux_head);
> + aux_head = rb->user_page->aux_head = rb->aux_head;
>
> - if (aux_head - local_read(&rb->aux_wakeup) >= rb->aux_watermark) {
> + if (aux_head - rb->aux_wakeup >= rb->aux_watermark) {
Can't we just do away with aux_head here:
rb->user_page->aux_head = rb->aux_head;
if (rb->aux_head - rb->aux_wakeup >= rb->aux_watermark) { ...
?
> @@ -485,14 +485,13 @@ int perf_aux_output_skip(struct perf_output_handle
> *handle, unsigned long size)
> if (size > handle->size)
> return -ENOSPC;
>
> - local_add(size, &rb->aux_head);
> + rb->aux_head += size;
>
> - aux_head = rb->user_page->aux_head = local_read(&rb->aux_head);
> - if (aux_head - local_read(&rb->aux_wakeup) >= rb->aux_watermark) {
> + aux_head = rb->user_page->aux_head = rb->aux_head;
> + if (aux_head - rb->aux_wakeup >= rb->aux_watermark) {
> perf_output_wakeup(handle);
> - local_add(rb->aux_watermark, &rb->aux_wakeup);
> - handle->wakeup = local_read(&rb->aux_wakeup) +
> - rb->aux_watermark;
> + rb->aux_wakeup += rb->aux_watermark;
> + handle->wakeup = rb->aux_wakeup + rb->aux_watermark;
> }
>
> handle->head = aux_head;
And here I think we don't need aux_head at all.
Thanks,
--
Alex
