Merge branch 't/map_populate'

diff --git a/NEWS b/NEWS
index 6db7225350f014f80e3f0ad831fe60b93d2777b9..3a7027298f5a20ee00793554b2be89a997f331c3 100644 (file)
--- 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 f6da52dd6cc933f66a746095389ad1510452d0e4..e336a9e7413d469c71a6221cab0e86b0aae24867 100644 (file)
--- 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;
+               }
        }
 }