@@ -629,6 +629,19 @@ if test "$build_pcm_mmap_emul" = "yes"; then
AC_DEFINE([BUILD_PCM_PLUGIN_MMAP_EMUL], "1", [Build PCM mmap-emul plugin])
fi
+if test "$build_pcm_dmix" = "yes"; then
+AC_MSG_CHECKING(for default lockless dmix)
+AC_ARG_ENABLE(lockless-dmix,
+ AS_HELP_STRING([--enable-lockless-dmix],
+ [use lockless dmix as default on x86]),
+ lockless_dmix="$enableval", lockless_dmix="no")
+if test "$lockless_dmix" = "yes"; then
+ AC_MSG_RESULT(yes)
+ AC_DEFINE([LOCKLESS_DMIX_DEFAULT], "1", [Lockless dmix as default])
+else
+ AC_MSG_RESULT(no)
+fi
+fi
dnl Create PCM plugin symbol list for static library
rm -f "$srcdir"/src/pcm/pcm_symbols_list.c
@@ -82,7 +82,13 @@ int snd_pcm_direct_semaphore_create_or_connect(snd_pcm_direct_t *dmix)
return 0;
}
-#define SND_PCM_DIRECT_MAGIC (0xa15ad300 + sizeof(snd_pcm_direct_share_t))
+static unsigned int snd_pcm_direct_magic(snd_pcm_direct_t *dmix)
+{
+ if (!dmix->direct_memory_access)
+ return 0xa15ad300 + sizeof(snd_pcm_direct_share_t);
+ else
+ return 0xb15ad300 + sizeof(snd_pcm_direct_share_t);
+}
/*
* global shared memory area
@@ -132,10 +138,10 @@ retryget:
buf.shm_perm.gid = dmix->ipc_gid;
shmctl(dmix->shmid, IPC_SET, &buf);
}
- dmix->shmptr->magic = SND_PCM_DIRECT_MAGIC;
+ dmix->shmptr->magic = snd_pcm_direct_magic(dmix);
return 1;
} else {
- if (dmix->shmptr->magic != SND_PCM_DIRECT_MAGIC) {
+ if (dmix->shmptr->magic != snd_pcm_direct_magic(dmix)) {
snd_pcm_direct_shm_discard(dmix);
return -EINVAL;
}
@@ -1892,7 +1898,11 @@ int snd_pcm_direct_parse_open_conf(snd_config_t *root, snd_config_t *conf,
rec->slowptr = 1;
rec->max_periods = 0;
rec->var_periodsize = 0;
+#ifdef LOCKLESS_DMIX_DEFAULT
rec->direct_memory_access = 1;
+#else
+ rec->direct_memory_access = 0;
+#endif
rec->hw_ptr_alignment = SND_PCM_HW_PTR_ALIGNMENT_AUTO;
rec->tstamp_type = -1;
The recently reported (but a long-standing) bug about the unconditional semaphore usage in the dmix implies that basically we've had no problem with the locking in the practical usages over years. Although the lockless operation has a clear merit, it's a much higher CPU usage (especially on some uncached pages), and it might lead to a potential deadlock in theory (which is hard to reproduce at will, though). This patch introduces a new configure option "--enable-lockless-dmix" or "--disable-lockless-dmix" to let user choose the default dmix operation mode. The usage of the lockless mixing has been already conditionally enabled via asoundrc and card config "direct_memory_access", so we just need to set the default value based on it. In this patch, the default is set off to the lockless mixing, i.e. the generic mixing is chosen. It makes more sense from the performance POV. For any users who still require the lockless operation, it can be enabled either via configure option or the asoundrc. The magic number used in the shmem is also changed depending on the operation mode. It's just for safety, not to conflict both operation modes with each other. Signed-off-by: Takashi Iwai <tiwai@suse.de> --- configure.ac | 13 +++++++++++++ src/pcm/pcm_direct.c | 16 +++++++++++++--- 2 files changed, 26 insertions(+), 3 deletions(-)