UbiquitousOS
/
OpenCloudOS-Kernel
mirror of https://gitee.com/OpenCloudOS/OpenCloudOS-Kernel.git
11
0
Fork 0
Code Issues Projects Releases Wiki Activity

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>
This commit is contained in:
Clemens Ladisch 2009-01-26 08:09:28 +01:00 committed by Takashi Iwai
parent b7eb4a06e9
commit 4d788e040b
1 changed files with 8 additions and 1 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

9
sound/usb/usbaudio.c
View File

@ -108,6 +108,7 @@ MODULE_PARM_DESC(ignore_ctl_error,
#define MAX_URBS 8
#define SYNC_URBS 4 /* always four urbs for sync */
#define MIN_PACKS_URB 1 /* minimum 1 packet per urb */
#define MAX_QUEUE 24 /* try not to exceed this queue length, in ms */
struct audioformat {
struct list_head list;
@ -1079,7 +1080,7 @@ static int init_substream_urbs(struct snd_usb_substream *subs, unsigned int peri
/* decide how many packets to be used */
if (is_playback) {
unsigned int minsize;
unsigned int minsize, maxpacks;
/* determine how small a packet can be */
minsize = (subs->freqn >> (16 - subs->datainterval))
* (frame_bits >> 3);
@ -1094,6 +1095,12 @@ static int init_substream_urbs(struct snd_usb_substream *subs, unsigned int peri
/* we need at least two URBs for queueing */
if (total_packs < 2 * MIN_PACKS_URB * packs_per_ms)
total_packs = 2 * MIN_PACKS_URB * packs_per_ms;
else {
/* and we don't want too long a queue either */
maxpacks = max((unsigned int)MAX_QUEUE, urb_packs * 2);
if (total_packs > maxpacks * packs_per_ms)
total_packs = maxpacks * packs_per_ms;
}
} else {
total_packs = MAX_URBS * urb_packs;
}