[ALSA] usb-audio: optimize handling of capture URBs

USB generic driver
When preparing capture URBs, we don't need to stop when we cross a
period boundary because we now never handle more than one millisecond of
data per URB anyway.

When handling captured data, use an extra flag to call
snd_pcm_period_elapsed() no more than once.  This allows us to move the
period boundary checking code before the copying of the data which
avoids a second locking of the substream's lock.

Signed-off-by: Clemens Ladisch <clemens@ladisch.de>

diff --git a/sound/usb/usbaudio.c b/sound/usb/usbaudio.c
index a62d131..a703d96 100644 (file)
--- a/sound/usb/usbaudio.c
+++ b/sound/usb/usbaudio.c
@@ -311,27 +311,18 @@ static int prepare_capture_urb(snd_usb_substream_t *subs,
                               struct urb *urb)
 {
        int i, offs;
-       unsigned long flags;
        snd_urb_ctx_t *ctx = (snd_urb_ctx_t *)urb->context;
 
        offs = 0;
        urb->dev = ctx->subs->dev; /* we need to set this at each time */
-       urb->number_of_packets = 0;
-       spin_lock_irqsave(&subs->lock, flags);
        for (i = 0; i < ctx->packets; i++) {
                urb->iso_frame_desc[i].offset = offs;
                urb->iso_frame_desc[i].length = subs->curpacksize;
                offs += subs->curpacksize;
-               urb->number_of_packets++;
-               subs->transfer_sched += subs->curframesize;
-               if (subs->transfer_sched >= runtime->period_size) {
-                       subs->transfer_sched -= runtime->period_size;
-                       break;
-               }
        }
-       spin_unlock_irqrestore(&subs->lock, flags);
        urb->transfer_buffer = ctx->buf;
        urb->transfer_buffer_length = offs;
+       urb->number_of_packets = ctx->packets;
 #if 0 // for check
        if (! urb->bandwidth) {
                int bustime;
@@ -359,6 +350,7 @@ static int retire_capture_urb(snd_usb_substream_t *subs,
        unsigned char *cp;
        int i;
        unsigned int stride, len, oldptr;
+       int period_elapsed = 0;
 
        stride = runtime->frame_bits >> 3;
 
@@ -378,6 +370,10 @@ static int retire_capture_urb(snd_usb_substream_t *subs,
                if (subs->hwptr_done >= runtime->buffer_size)
                        subs->hwptr_done -= runtime->buffer_size;
                subs->transfer_done += len;
+               if (subs->transfer_done >= runtime->period_size) {
+                       subs->transfer_done -= runtime->period_size;
+                       period_elapsed = 1;
+               }
                spin_unlock_irqrestore(&subs->lock, flags);
                /* copy a data chunk */
                if (oldptr + len > runtime->buffer_size) {
@@ -388,15 +384,9 @@ static int retire_capture_urb(snd_usb_substream_t *subs,
                } else {
                        memcpy(runtime->dma_area + oldptr * stride, cp, len * stride);
                }
-               /* update the pointer, call callback if necessary */
-               spin_lock_irqsave(&subs->lock, flags);
-               if (subs->transfer_done >= runtime->period_size) {
-                       subs->transfer_done -= runtime->period_size;
-                       spin_unlock_irqrestore(&subs->lock, flags);
-                       snd_pcm_period_elapsed(subs->pcm_substream);
-               } else
-                       spin_unlock_irqrestore(&subs->lock, flags);
        }
+       if (period_elapsed)
+               snd_pcm_period_elapsed(subs->pcm_substream);
        return 0;
 }