On Mon, Jul 31, 2017 at 01:28:01PM +0300, Alexander Shishkin wrote: > Will Deacon <[email protected]> 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.
Agreed on both counts. Will fix for v2. Will
