| Message ID | 1501260863-14687-1-git-send-email-will.deacon@arm.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Will Deacon <will.deacon@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
On Mon, Jul 31, 2017 at 01:28:01PM +0300, Alexander Shishkin wrote: > Will Deacon <will.deacon@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. Agreed on both counts. Will fix for v2. Will
diff --git a/kernel/events/internal.h b/kernel/events/internal.h index 486fd78eb8d5..2941b868353c 100644 --- a/kernel/events/internal.h +++ b/kernel/events/internal.h @@ -38,9 +38,9 @@ struct ring_buffer { struct user_struct *mmap_user; /* AUX area */ - local_t aux_head; + long aux_head; local_t aux_nest; - local_t aux_wakeup; + long aux_wakeup; unsigned long aux_pgoff; int aux_nr_pages; int aux_overwrite; diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c index 14a240ff439d..330df5a7f762 100644 --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -367,7 +367,7 @@ void *perf_aux_output_begin(struct perf_output_handle *handle, if (WARN_ON_ONCE(local_xchg(&rb->aux_nest, 1))) goto err_put; - aux_head = local_read(&rb->aux_head); + aux_head = rb->aux_head; handle->rb = rb; handle->event = event; @@ -382,7 +382,7 @@ void *perf_aux_output_begin(struct perf_output_handle *handle, */ if (!rb->aux_overwrite) { aux_tail = ACCESS_ONCE(rb->user_page->aux_tail); - handle->wakeup = local_read(&rb->aux_wakeup) + rb->aux_watermark; + handle->wakeup = rb->aux_wakeup + rb->aux_watermark; if (aux_head - aux_tail < perf_aux_size(rb)) handle->size = CIRC_SPACE(aux_head, aux_tail, perf_aux_size(rb)); @@ -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) { wakeup = true; - local_add(rb->aux_watermark, &rb->aux_wakeup); + rb->aux_wakeup += rb->aux_watermark; } if (wakeup) { @@ -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;
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. Cc: Mark Rutland <mark.rutland@arm.com> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Will Deacon <will.deacon@arm.com> --- kernel/events/internal.h | 4 ++-- kernel/events/ring_buffer.c | 27 +++++++++++++-------------- 2 files changed, 15 insertions(+), 16 deletions(-)