From: Andre Noll <maan@systemlinux.org>
Date: Mon, 24 Oct 2011 13:31:31 +0000 (+0200)
Subject: Merge branch 't/map_populate'
X-Git-Tag: v0.4.9~15
X-Git-Url: http://git.tuebingen.mpg.de/?p=paraslash.git;a=commitdiff_plain;h=a5ad3d4c598bafe28e90e5b623e0a754d6e973d5;hp=b307a25ed895caa33684302b502e9e0e70dc78b7

Merge branch 't/map_populate'
---

diff --git a/NEWS b/NEWS
index 6db72253..3a702729 100644
--- a/NEWS
+++ b/NEWS
@@ -9,6 +9,8 @@
 	- Shared memory areas are no longer restricted to 64K. We now
 	  detect the maximal size of a shared memory area at runtime.
 	- cleanup of the internal uptime API.
+	- para_server prefaults the mmapped audio file to avoid
+	  delays on slow media.
 
 --------------------------------------
 0.4.8 (2011-08-19) "nested assignment"
diff --git a/vss.c b/vss.c
index f6da52dd..e336a9e7 100644
--- a/vss.c
+++ b/vss.c
@@ -953,6 +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;
@@ -987,8 +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);
@@ -1077,6 +1081,23 @@ static void vss_send(struct vss_task *vsst)
 		}
 		mmd->chunks_sent++;
 		mmd->current_chunk++;
+		/*
+		 * 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.
+		 */
+		buf += len;
+		for (i = 0; i < 5 && buf < vsst->map + mmd->size; i++) {
+			__a_unused volatile char x = *buf;
+			buf += 4096;
+		}
 	}
 }