[ALSA] usb-audio: schedule high speed URBs with 1 ms alignment
USB generic driver
The EHCI driver doesn't interrupt more than once per millisecond, and
organizes all iso transfers with frame-sized ITDs, so we can (try to)
be more efficient by aligning all URBs on frame boundaries.
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
diff --git a/sound/usb/usbaudio.c b/sound/usb/usbaudio.c
index 49075f0..a62d131 100644
--- a/sound/usb/usbaudio.c
+++ b/sound/usb/usbaudio.c
@@ -893,7 +893,7 @@
{
unsigned int maxsize, n, i;
int is_playback = subs->direction == SNDRV_PCM_STREAM_PLAYBACK;
- unsigned int npacks[MAX_URBS], urb_packs, total_packs;
+ unsigned int npacks[MAX_URBS], urb_packs, total_packs, packs_per_ms;
/* calculate the frequency in 16.16 format */
if (snd_usb_get_speed(subs->dev) == USB_SPEED_FULL)
@@ -920,14 +920,18 @@
else
subs->curpacksize = maxsize;
+ if (snd_usb_get_speed(subs->dev) == USB_SPEED_HIGH)
+ packs_per_ms = 8 >> subs->datainterval;
+ else
+ packs_per_ms = 1;
+
if (is_playback) {
urb_packs = nrpacks;
urb_packs = max(urb_packs, (unsigned int)MIN_PACKS_URB);
urb_packs = min(urb_packs, (unsigned int)MAX_PACKS);
} else
urb_packs = 1;
- if (snd_usb_get_speed(subs->dev) == USB_SPEED_HIGH)
- urb_packs = (urb_packs * 8) >> subs->datainterval;
+ urb_packs *= packs_per_ms;
/* allocate a temporary buffer for playback */
if (is_playback) {
@@ -949,8 +953,12 @@
minsize -= minsize >> 2;
minsize = max(minsize, 1u);
total_packs = (period_bytes + minsize - 1) / minsize;
- if (total_packs < 2 * MIN_PACKS_URB)
- total_packs = 2 * MIN_PACKS_URB;
+ /* round up to multiple of packs_per_ms */
+ total_packs = (total_packs + packs_per_ms - 1)
+ & ~(packs_per_ms - 1);
+ /* 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 {
total_packs = MAX_URBS * urb_packs;
}
@@ -972,7 +980,7 @@
subs->nurbs = 2;
npacks[0] = (total_packs + 1) / 2;
npacks[1] = total_packs - npacks[0];
- } else if (npacks[subs->nurbs-1] < MIN_PACKS_URB) {
+ } else if (npacks[subs->nurbs-1] < MIN_PACKS_URB * packs_per_ms) {
/* the last packet is too small.. */
if (subs->nurbs > 2) {
/* merge to the first one */