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authorClemens Ladisch <clemens@ladisch.de>2009-01-26 02:09:28 -0500
committerTakashi Iwai <tiwai@suse.de>2009-01-26 11:05:07 -0500
commit4d788e040b72d2a46ea3ba726b7fa0b65de06c88 (patch)
tree8cc83947a001100f9f551bbe555322646d43f42f /sound/usb/usbaudio.c
parentb7eb4a06e9980973755b7e95a6d97fb8decbf8fd (diff)
sound: usb-audio: limit playback queue length
Once our URBs contain enough packets, queueing more URBs does not give us any additional underrun protection (as we use double-buffering) but just increases latency unnecessarily. Therefore, we try to limit the queue length to some reasonable value. Signed-off-by: Clemens Ladisch <clemens@ladisch.de> Signed-off-by: Takashi Iwai <tiwai@suse.de>
Diffstat (limited to 'sound/usb/usbaudio.c')
-rw-r--r--sound/usb/usbaudio.c9
1 files changed, 8 insertions, 1 deletions
diff --git a/sound/usb/usbaudio.c b/sound/usb/usbaudio.c
index 417d557ed641..f3d4de23fedf 100644
--- a/sound/usb/usbaudio.c
+++ b/sound/usb/usbaudio.c
@@ -108,6 +108,7 @@ MODULE_PARM_DESC(ignore_ctl_error,
108#define MAX_URBS 8 108#define MAX_URBS 8
109#define SYNC_URBS 4 /* always four urbs for sync */ 109#define SYNC_URBS 4 /* always four urbs for sync */
110#define MIN_PACKS_URB 1 /* minimum 1 packet per urb */ 110#define MIN_PACKS_URB 1 /* minimum 1 packet per urb */
111#define MAX_QUEUE 24 /* try not to exceed this queue length, in ms */
111 112
112struct audioformat { 113struct audioformat {
113 struct list_head list; 114 struct list_head list;
@@ -1079,7 +1080,7 @@ static int init_substream_urbs(struct snd_usb_substream *subs, unsigned int peri
1079 1080
1080 /* decide how many packets to be used */ 1081 /* decide how many packets to be used */
1081 if (is_playback) { 1082 if (is_playback) {
1082 unsigned int minsize; 1083 unsigned int minsize, maxpacks;
1083 /* determine how small a packet can be */ 1084 /* determine how small a packet can be */
1084 minsize = (subs->freqn >> (16 - subs->datainterval)) 1085 minsize = (subs->freqn >> (16 - subs->datainterval))
1085 * (frame_bits >> 3); 1086 * (frame_bits >> 3);
@@ -1094,6 +1095,12 @@ static int init_substream_urbs(struct snd_usb_substream *subs, unsigned int peri
1094 /* we need at least two URBs for queueing */ 1095 /* we need at least two URBs for queueing */
1095 if (total_packs < 2 * MIN_PACKS_URB * packs_per_ms) 1096 if (total_packs < 2 * MIN_PACKS_URB * packs_per_ms)
1096 total_packs = 2 * MIN_PACKS_URB * packs_per_ms; 1097 total_packs = 2 * MIN_PACKS_URB * packs_per_ms;
1098 else {
1099 /* and we don't want too long a queue either */
1100 maxpacks = max((unsigned int)MAX_QUEUE, urb_packs * 2);
1101 if (total_packs > maxpacks * packs_per_ms)
1102 total_packs = maxpacks * packs_per_ms;
1103 }
1097 } else { 1104 } else {
1098 total_packs = MAX_URBS * urb_packs; 1105 total_packs = MAX_URBS * urb_packs;
1099 } 1106 }