diff options
| -rw-r--r-- | include/uapi/linux/perf_event.h | 1 | ||||
| -rw-r--r-- | kernel/events/internal.h | 1 | ||||
| -rw-r--r-- | kernel/events/ring_buffer.c | 48 |
3 files changed, 35 insertions, 15 deletions
diff --git a/include/uapi/linux/perf_event.h b/include/uapi/linux/perf_event.h index 8904ad3a850b..29ef2f73bb4a 100644 --- a/include/uapi/linux/perf_event.h +++ b/include/uapi/linux/perf_event.h @@ -803,6 +803,7 @@ enum perf_callchain_context { * PERF_RECORD_AUX::flags bits */ #define PERF_AUX_FLAG_TRUNCATED 0x01 /* record was truncated to fit */ +#define PERF_AUX_FLAG_OVERWRITE 0x02 /* snapshot from overwrite mode */ #define PERF_FLAG_FD_NO_GROUP (1UL << 0) #define PERF_FLAG_FD_OUTPUT (1UL << 1) diff --git a/kernel/events/internal.h b/kernel/events/internal.h index b701ebc32570..ffd51d9f5945 100644 --- a/kernel/events/internal.h +++ b/kernel/events/internal.h @@ -40,6 +40,7 @@ struct ring_buffer { local_t aux_nest; unsigned long aux_pgoff; int aux_nr_pages; + int aux_overwrite; atomic_t aux_mmap_count; unsigned long aux_mmap_locked; void (*free_aux)(void *); diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c index 0cc7b0f39058..67b328337a41 100644 --- a/kernel/events/ring_buffer.c +++ b/kernel/events/ring_buffer.c @@ -283,26 +283,33 @@ void *perf_aux_output_begin(struct perf_output_handle *handle, goto err_put; aux_head = local_read(&rb->aux_head); - aux_tail = ACCESS_ONCE(rb->user_page->aux_tail); handle->rb = rb; handle->event = event; handle->head = aux_head; - if (aux_head - aux_tail < perf_aux_size(rb)) - handle->size = CIRC_SPACE(aux_head, aux_tail, perf_aux_size(rb)); - else - handle->size = 0; + handle->size = 0; /* - * handle->size computation depends on aux_tail load; this forms a - * control dependency barrier separating aux_tail load from aux data - * store that will be enabled on successful return + * In overwrite mode, AUX data stores do not depend on aux_tail, + * therefore (A) control dependency barrier does not exist. The + * (B) <-> (C) ordering is still observed by the pmu driver. */ - if (!handle->size) { /* A, matches D */ - event->pending_disable = 1; - perf_output_wakeup(handle); - local_set(&rb->aux_nest, 0); - goto err_put; + if (!rb->aux_overwrite) { + aux_tail = ACCESS_ONCE(rb->user_page->aux_tail); + if (aux_head - aux_tail < perf_aux_size(rb)) + handle->size = CIRC_SPACE(aux_head, aux_tail, perf_aux_size(rb)); + + /* + * handle->size computation depends on aux_tail load; this forms a + * control dependency barrier separating aux_tail load from aux data + * store that will be enabled on successful return + */ + if (!handle->size) { /* A, matches D */ + event->pending_disable = 1; + perf_output_wakeup(handle); + local_set(&rb->aux_nest, 0); + goto err_put; + } } return handle->rb->aux_priv; @@ -327,13 +334,22 @@ void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size, bool truncated) { struct ring_buffer *rb = handle->rb; - unsigned long aux_head = local_read(&rb->aux_head); + unsigned long aux_head; u64 flags = 0; if (truncated) flags |= PERF_AUX_FLAG_TRUNCATED; - local_add(size, &rb->aux_head); + /* in overwrite mode, driver provides aux_head via handle */ + if (rb->aux_overwrite) { + flags |= PERF_AUX_FLAG_OVERWRITE; + + aux_head = handle->head; + local_set(&rb->aux_head, aux_head); + } else { + aux_head = local_read(&rb->aux_head); + local_add(size, &rb->aux_head); + } if (size || flags) { /* @@ -480,6 +496,8 @@ int rb_alloc_aux(struct ring_buffer *rb, struct perf_event *event, */ atomic_set(&rb->aux_refcount, 1); + rb->aux_overwrite = overwrite; + out: if (!ret) rb->aux_pgoff = pgoff; |