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Commit b263a9bd authored by Clemens Ladisch's avatar Clemens Ladisch Committed by Jaroslav Kysela
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[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: default avatarClemens Ladisch <clemens@ladisch.de>
parent 99250872

sound/usb/usbaudio.c

+8 −18
Original line number Diff line number Diff line
@@ -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;

}