Performance: cache the backend pages pointer in context

[lttng-ust.git] / libringbuffer / backend_internal.h

diff --git a/libringbuffer/backend_internal.h b/libringbuffer/backend_internal.h
index 9edd2e59f8b348bc5f8352e589d3499fcb0f476d..90088b89c7a8ffbfb81eac3efedad3cbefbb6f8e 100644 (file)
--- a/libringbuffer/backend_internal.h
+++ b/libringbuffer/backend_internal.h
@@ -196,6 +196,53 @@ int subbuffer_id_check_index(const struct lttng_ust_lib_ring_buffer_config *conf
                return 0;
 }
 
+static inline
+int lib_ring_buffer_backend_get_pages(const struct lttng_ust_lib_ring_buffer_config *config,
+                       struct lttng_ust_lib_ring_buffer_ctx *ctx,
+                       struct lttng_ust_lib_ring_buffer_backend_pages **backend_pages)
+{
+       struct lttng_ust_lib_ring_buffer_backend *bufb = &ctx->buf->backend;
+       struct channel_backend *chanb = &ctx->chan->backend;
+       struct lttng_ust_shm_handle *handle = ctx->handle;
+       size_t sbidx;
+       size_t offset = ctx->buf_offset;
+       struct lttng_ust_lib_ring_buffer_backend_subbuffer *wsb;
+       struct lttng_ust_lib_ring_buffer_backend_pages_shmp *rpages;
+       unsigned long sb_bindex, id;
+       struct lttng_ust_lib_ring_buffer_backend_pages *_backend_pages;
+
+       offset &= chanb->buf_size - 1;
+       sbidx = offset >> chanb->subbuf_size_order;
+       wsb = shmp_index(handle, bufb->buf_wsb, sbidx);
+       if (caa_unlikely(!wsb))
+               return -1;
+       id = wsb->id;
+       sb_bindex = subbuffer_id_get_index(config, id);
+       rpages = shmp_index(handle, bufb->array, sb_bindex);
+       if (caa_unlikely(!rpages))
+               return -1;
+       CHAN_WARN_ON(ctx->chan,
+                    config->mode == RING_BUFFER_OVERWRITE
+                    && subbuffer_id_is_noref(config, id));
+       _backend_pages = shmp(handle, rpages->shmp);
+       if (caa_unlikely(!_backend_pages))
+               return -1;
+       *backend_pages = _backend_pages;
+       return 0;
+}
+
+/* Get backend pages from cache. */
+static inline
+struct lttng_ust_lib_ring_buffer_backend_pages *
+       lib_ring_buffer_get_backend_pages_from_ctx(const struct lttng_ust_lib_ring_buffer_config *config,
+               struct lttng_ust_lib_ring_buffer_ctx *ctx)
+{
+       if (caa_unlikely(ctx->ctx_len
+                       < sizeof(struct lttng_ust_lib_ring_buffer_ctx)))
+               return NULL;
+       return ctx->backend_pages;
+}
+
 /*
  * The ring buffer can count events recorded and overwritten per buffer,
  * but it is disabled by default due to its performance overhead.