X-Git-Url: http://git.tuebingen.mpg.de/?a=blobdiff_plain;f=vss.c;h=db1beeba17d080e08f306830bc0ce9dd0b7bf5e0;hb=71bcf40d3aeed43884c8db9e44d5eade41f22db2;hp=b9afc8ed637374c82918f3448695a1a2fdaa94a2;hpb=82d08fb6da4dfc7d93d1ee0cce4706721378fe12;p=paraslash.git

diff --git a/vss.c b/vss.c
index b9afc8ed..db1beeba 100644
--- a/vss.c
+++ b/vss.c
@@ -132,6 +132,7 @@ struct fec_group {
 	uint16_t slice_bytes;
 };
 
+/** A FEC client is always in one of these states. */
 enum fec_client_state {
 	FEC_STATE_NONE = 0,	/**< not initialized and not enabled */
 	FEC_STATE_DISABLED,	/**< temporarily disabled */
@@ -952,6 +953,10 @@ static int recv_afs_msg(int afs_socket, int *fd, uint32_t *code, uint32_t *data)
 	return 1;
 }
 
+#ifndef MAP_POPULATE
+#define MAP_POPULATE 0
+#endif
+
 static void recv_afs_result(struct vss_task *vsst, fd_set *rfds)
 {
 	int ret, passed_fd, shmid;
@@ -986,8 +991,8 @@ static void recv_afs_result(struct vss_task *vsst, fd_set *rfds)
 	}
 	mmd->size = statbuf.st_size;
 	mmd->mtime = statbuf.st_mtime;
-	ret = para_mmap(mmd->size, PROT_READ, MAP_PRIVATE, passed_fd,
-		0, &vsst->map);
+	ret = para_mmap(mmd->size, PROT_READ, MAP_PRIVATE | MAP_POPULATE,
+		passed_fd, 0, &vsst->map);
 	if (ret < 0)
 		goto err;
 	close(passed_fd);
@@ -1074,6 +1079,25 @@ static void vss_send(struct vss_task *vsst)
 			senders[i].send(mmd->current_chunk, mmd->chunks_sent,
 				buf, len, vsst->header_buf, vsst->header_len);
 		}
+		/*
+		 * Prefault next chunk(s)
+		 *
+		 * If the backing device of the memory-mapped audio file is
+		 * slow and read-ahead is turned off or prevented for some
+		 * reason, e.g. due to memory pressure, it may take much longer
+		 * than the chunk interval to get the next chunk on the wire,
+		 * causing buffer underruns on the client side. Mapping the
+		 * file with MAP_POPULATE seems to help a bit, but it does not
+		 * eliminate the delays completely. Moreover, it is supported
+		 * only on Linux. So we do our own read-ahead here.
+		 */
+		if (mmd->current_chunk > 0) { /* chunk 0 might be on the heap */
+			buf += len;
+			for (i = 0; i < 5 && buf < vsst->map + mmd->size; i++) {
+				__a_unused volatile char x = *buf;
+				buf += 4096;
+			}
+		}
 		mmd->chunks_sent++;
 		mmd->current_chunk++;
 	}