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| author | Clemens Ladisch <clemens@ladisch.de> | 2009-01-26 08:09:28 +0100 |
|---|---|---|
| committer | Takashi Iwai <tiwai@suse.de> | 2009-01-26 17:05:07 +0100 |
| commit | 4d788e040b72d2a46ea3ba726b7fa0b65de06c88 (patch) | |
| tree | 8cc83947a001100f9f551bbe555322646d43f42f /sound/usb | |
| parent | b7eb4a06e9980973755b7e95a6d97fb8decbf8fd (diff) | |
| download | linux-4d788e040b72d2a46ea3ba726b7fa0b65de06c88.tar.gz | |
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')
| -rw-r--r-- | sound/usb/usbaudio.c | 9 |
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, #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; } |