[alsa-devel] Heavy looping inside snd_pcm_dmix_sync_area with snd_pcm_sw_params_set_stop_threshold > boundary and several hours of play
Adarsh
punia.adarsh at gmail.com
Tue Feb 18 15:02:29 CET 2014
Hi,
We are using RW_INTERLEAVED access as described in write_loop method in
/test/pcm.c and opening 'default' device.
However to disable the underruns, the snd_pcm_sw_params_set_stop_threshold
is set to 0x7fffffff which is greater than boundary
value. Period size is 1024 and buffer size is 2048. We try to write
period_size no of frames using snd_pcm_writei.
This setup runs fine for several hours. It was left runing overnight. After
some 12 hours of play, gdb is attached to the process and continued inside
gdb.
At this point, the thread went into a tight loop taking >100% cpu and
playing same sound over and over again abusing speakers.
It did not recover for a long time.
Stack trace shows that 'snd_pcm_dmix_sync_area' in pcm_dmix.c is taking a
very long time to return because the 'size' is
a large unsinged interger and mix_areas is getting called with 'transfer'
value of <=2048.
Below is the stack trace:
(gdb) bt
#0 0xb7c44463 in mix_areas_32_smp (size=1360, dst=0xb6855000,
src=0x84a7510, sum=0xb6845000, dst_step=4, src_step=4, sum_step=4) at
pcm_dmix_i386.h:261
#1 0xb7c44d2b in mix_areas (dmix=0x84a7110, src_areas=0x84a51d0,
dst_areas=0x84a6f00, src_ofs=0, dst_ofs=7168, size=1024) at pcm_dmix.c:193
#2 0xb7c45422 in snd_pcm_dmix_sync_area (pcm=0x84a71e0) at pcm_dmix.c:371
#3 0xb7c46680 in snd_pcm_dmix_mmap_commit (pcm=0x84a71e0, offset=0,
size=1024) at pcm_dmix.c:813
#4 0xb7c07033 in snd_pcm_mmap_commit (pcm=0x84a71e0, offset=0,
frames=1024) at pcm.c:6501
#5 0xb7c1804e in snd_pcm_plugin_mmap_commit (pcm=0x84a6d18, offset=0,
size=1024) at pcm_plugin.c:434
#6 0xb7c07033 in snd_pcm_mmap_commit (pcm=0x84a6d18, offset=0,
frames=1024) at pcm.c:6501
#7 0xb7c17956 in snd_pcm_plugin_write_areas (pcm=0x84a5390,
areas=0xb68362b0, offset=0, size=1024) at pcm_plugin.c:290
#8 0xb7c074bb in snd1_pcm_write_areas (pcm=0x84a5390, areas=0xb68362b0,
offset=0, size=1024, func=0xb7c177fc <snd_pcm_plugin_write_areas>) at
pcm.c:6667
#9 0xb7c17cd5 in snd_pcm_plugin_writei (pcm=0x84a5390, buffer=0x84ab518,
size=1024) at pcm_plugin.c:361
#10 0xb7bff1a7 in _snd_pcm_writei (pcm=0x84a6b18, buffer=0x84ab518,
size=1024) at pcm_local.h:516
#11 0xb7bff16c in snd_pcm_writei (pcm=0x84a6b18, buffer=0x84ab518,
size=1024) at pcm.c:1258
(gdb) f 2
#2 0xb7c45422 in snd_pcm_dmix_sync_area (pcm=0x84a71e0) at pcm_dmix.c:371
371 pcm_dmix.c: No such file or directory.
(gdb) info locals
dmix = 0x84a7110
slave_hw_ptr = 234156032
slave_appl_ptr = 7168
slave_size = 1057171456
appl_ptr = 0
size = 1018295296
transfer = 1024
src_areas = 0x84a51d0
dst_areas = 0x84a6f00
(gdb) p *dmix
$1 = {type = SND_PCM_TYPE_DMIX, ipc_key = 5678293, ipc_perm = 432,
ipc_gid = 17, semid = 32768, shmid = 65536, shmptr = 0xb6859000, spcm =
0x84a7340,
appl_ptr = 217121792, last_appl_ptr = 233882624, hw_ptr = 233875428,
avail_max = 0, slave_appl_ptr = 234156032, slave_hw_ptr = 234147996,
slave_period_size = 1024, slave_buffer_size = 8192, slave_boundary =
1073741824, sync_ptr = 0xb7c4557c <snd_pcm_dmix_sync_ptr>,
state = SND_PCM_STATE_RUNNING, trigger_tstamp = {tv_sec = 1392384066,
tv_nsec = 8308000}, server = 0, client = 0, comm_fd = 0, hw_fd = 4,
timer_fd = {
fd = 3, events = 41, revents = 0}, poll_fd = 3, tread = 1,
timer_need_poll = 0, timer_event_suspend = 131072, timer_event_resume =
262144,
server_fd = 0, server_pid = 0, timer = 0x8496b90, interleaved = 1,
slowptr = 1, max_periods = 0, channels = 2, bindings = 0x0, u = {dmix = {
shmid_sum = 98305, sum_buffer = 0xb6837000, mix_areas_16 = 0xb7c443a8
<mix_areas_16_smp_mmx>, mix_areas_32 = 0xb7c44415 <mix_areas_32_smp>,
mix_areas_24 = 0xb7c4451b <mix_areas_24_smp_cmov>, mix_areas_u8 = 0,
remix_areas_16 = 0xb7c44638 <remix_areas_16_smp_mmx>,
remix_areas_32 = 0xb7c446a5 <remix_areas_32_smp>, remix_areas_24 =
0xb7c447ab <remix_areas_24_smp_cmov>, remix_areas_u8 = 0},
dsnoop = {<No data fields>}, dshare = {chn_mask =
13151478482154389505}}, server_free = 0}
(gdb) p *pcm
$2 = {dl_handle = 0x0, name = 0x84a6e48 "dmix:0", type = SND_PCM_TYPE_DMIX,
stream = SND_PCM_STREAM_PLAYBACK, mode = 0, poll_fd_count = 1, poll_fd = 3,
poll_events = 1, setup = -1, monotonic = 0, access =
SND_PCM_ACCESS_MMAP_INTERLEAVED, format = SND_PCM_FORMAT_S32_LE, subformat
= SND_PCM_SUBFORMAT_STD,
channels = 2, rate = 44100, period_size = 1024, period_time = 23219,
periods = {min = 0, max = 0, openmin = 0, openmax = 0, integer = 0, empty =
0},
tstamp_mode = SND_PCM_TSTAMP_NONE, period_step = 1, avail_min = 1024,
period_event = 0, start_threshold = 1024, stop_threshold = 2147483647,
silence_threshold = 0, silence_size = 0, boundary = 1073741824, info =
2151743747, msbits = 32, rate_num = 44100, rate_den = 1, hw_flags = 0,
fifo_size = 0, buffer_size = 2048, buffer_time = {min = 0, max = 0,
openmin = 0, openmax = 0, integer = 0, empty = 0}, sample_bits = 32,
frame_bits = 64, appl = {master = 0x0, ptr = 0x84a7130, fd = -1, offset =
0, link_dst_count = 0, link_dst = 0x0, private_data = 0x0, changed = 0}, hw
= {
master = 0x0, ptr = 0x84a7138, fd = -1, offset = 0, link_dst_count = 0,
link_dst = 0x0, private_data = 0x0, changed = 0}, min_align = 1, mmap_rw =
1,
mmap_shadow = 0, donot_close = 0, mmap_channels = 0x84a54a0,
running_areas = 0x84a51d0, stopped_areas = 0x0, ops = 0xb7c91860, fast_ops
= 0xb7c918a0,
op_arg = 0x84a71e0, fast_op_arg = 0x84a71e0, private_data = 0x84a7110,
async_handlers = {next = 0x84a72e4, prev = 0x84a72e4}}
Attaching gdb does not show this behaviour if
snd_pcm_sw_params_set_stop_threshold is not set, which then defaults to
buffer size or when the
application is running for shorter duration.
Is it that setting of stop threshold to 0x7fffffff is triggering this and
attaching gdb is making the buffer pointers misbehave?
If so, what can be done if we do not want PCM to stop.
Below is the pcm dump:
Plug PCM: Linear conversion PCM (S32_LE)
Its setup is:
stream : PLAYBACK
access : RW_INTERLEAVED
format : S16_LE
subformat : STD
channels : 2
rate : 44100
exact rate : 44100 (44100/1)
msbits : 16
buffer_size : 2048
period_size : 1024
period_time : 23219
tstamp_mode : NONE
period_step : 1
avail_min : 1024
period_event : 0
start_threshold : 1024
stop_threshold : 2147483647
silence_threshold: 0
silence_size : 0
boundary : 1073741824
Slave: Soft volume PCM
Control: PCM Playback Volume
min_dB: -51
max_dB: 0
resolution: 256
Its setup is:
stream : PLAYBACK
access : MMAP_INTERLEAVED
format : S32_LE
subformat : STD
channels : 2
rate : 44100
exact rate : 44100 (44100/1)
msbits : 32
buffer_size : 2048
period_size : 1024
period_time : 23219
tstamp_mode : NONE
period_step : 1
avail_min : 1024
period_event : 0
start_threshold : 1024
stop_threshold : 2147483647
silence_threshold: 0
silence_size : 0
boundary : 1073741824
Slave: Direct Stream Mixing PCM
Its setup is:
stream : PLAYBACK
access : MMAP_INTERLEAVED
format : S32_LE
subformat : STD
channels : 2
rate : 44100
exact rate : 44100 (44100/1)
msbits : 32
buffer_size : 2048
period_size : 1024
period_time : 23219
tstamp_mode : NONE
period_step : 1
avail_min : 1024
period_event : 0
start_threshold : 1024
stop_threshold : 2147483647
silence_threshold: 0
silence_size : 0
boundary : 1073741824
Hardware PCM card 0 'HDA Intel PCH' device 0 subdevice 0
Its setup is:
stream : PLAYBACK
access : MMAP_INTERLEAVED
format : S32_LE
subformat : STD
channels : 2
rate : 44100
exact rate : 44100 (44100/1)
msbits : 32
buffer_size : 8192
period_size : 1024
period_time : 23219
tstamp_mode : ENABLE
period_step : 1
avail_min : 1024
period_event : 0
start_threshold : 1
stop_threshold : 1073741824
silence_threshold: 0
silence_size : 1073741824
boundary : 1073741824
appl_ptr : 0
hw_ptr : 0
Thanks
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